My main point is that you can't put this idea aside just because you don't like it and because it doesn't suit with the style of game you have decided Stellaris should be.
Your opinion is biased, and with the summary from legendsmith which is also biased, you try to lead Paradox's solution in your way. Who are you to decide that an idea is good or bad for the game?
Let's first address that, I don't put the idea aside because I don't like it. I put it aside because a.) it doesn't work without changing everything about warfare and b.) because the Devs made a deliberate decision not to limit the size of individual fleets and only put a very generous soft cap on the total number of ships you can have. You or I have no influence what so ever to lead Paradox towards anything, all we can do is make suggestions and try to make those suggestions as good as possible and as easy to implement as possible so maybe, just maybe, it gets picked up or inspires the developers to do something similar. In that light, suggestions that require a total rework of the combat system are unlikely to make it into the game and are therefore not good solutions to the problem. If a major overhaul of warfare happens, then the ideas in this thread may have a slight impact on the details, but only if they coincide with the vision the developers have of how combat should work.
If I criticize an idea and give reasons for why it wouldn't work in the current scope of the game, then you have to prove me wrong with counter arguments, not by ad hominem arguments. That only gives the impression that you have no substantial arguments you can bring.
First you must understand that losing an admiral in the middle of a battle and having no one to replace him/her puts you in serious trouble.
I never said anything about the admiral dying in a fight, there is ample time between fights an admiral could die. It also isn't relevant to the criticism. If an admiral dies, that commands a fleet of maximal size, any admiral you newly hire will be unable to command that fleet, because it exceeds the command limit. So what happens to the excess ships? They can't be part of that fleet anymore, so you would need to hire a second admiral, provided you have free slots and the influence to pay for a second one. I'm assuming the best case, and all the fleets the dead admiral controlled get an exception to the no admiral assignment outside your home system you introduced to prevent switching admirals around to circumvent the movement rule.
Then the rule would not be only "You must have an admiral". There should be some work on it, for example something in case you have only one admiral, who dies.
A rule that needs an exception to cover for a flaw is by definition not a good rule. Sometimes it's inevitable in a complex game to make such exceptions, but it should really only be done when absolutely necessary.
Now I'm going to demonstrate in detail why in the current state of Stellaris limited fleet sizes are not the answer.
[EDIT]There is a TL;DR at the end, so if you just want to know the point I'm making, you can skip my little play-by-play demonstrating it in detail.[/EDIT]
1. Fleet sized tied to admiral level and largest hull without mixed fleet requirements:
a.) Since the limit on how many ships can be in a fleet without an admiral can't be 0, there needs to exist a minimum fleet size, let's take 10 for corvettes, 15 for destroyer, 20 for cruiser and 25 for battle ships. An admiral adds 5 per level, so one admiral can command up to 35 corvettes or 50 battleships. This creates a problem, because why would you ever build corvettes if you have bigger ships available, that you could then also command more of. The only thing it creates are battleship doomstacks of 50 battleships, making the number smaller only shifts it around depending on which numbers you adjust. If you want more ships in a fleet, you'll add another admiral, limits doomstacks a bit because of the limit on leaders, but the difference between having 8 scientists, a governor and an admiral or having 7 scientists and 3 admirals doesn't really limit you much, making them smaller does change it a bit, but you would have to drop the limit way down, say only give 4 ships for battleships and 5 for max lvl admiral, so you get 9 battleships and a maximum of 6 corvettes. So that doesn't really work out too well.
b.) Instead have each ship cost their weight in fleet capacity. Those 50 slots from earlier now can only fit in 6 battleships plus one destroyer or two corvettes. So stacking battleships sounds like it's not a good idea anymore, still want that extra fleet size though. So new best solution, one battleship and 42 corvettes. Basically you now have the token battleship and a swarm of corvettes. And everyone else will use that exact same composition, because numbers trump quality. No matter how you slice it, you will always create an objectively best fleet composition. You can fiddle the numbers around however you like, it will always be slanted towards one extreme.
2. Fleet sized tied to admiral level and largest hull with mixed fleet requirements:
The previous example obviously doesn't work, so to make it more balanced a ratio between capital ships and escorts gets introduced. To make it easy, I'll just take the numbers from the recommended ratio in Hearts of Iron 4, that's 3 escorts for each capital ship.
a.) So the size limit of 50 if you have a battleship again, but now you can't just put 50 battleships in a fleet. We want to maximize our fleet power, so obviously we bring as many battleships as we can without exceeding that limit, that's 12 and 38 escorts. Now we don't want to use corvettes, because in this case destroyers give our fleet more power. So optimal solution 12 battleships 38destroyers, no cruisers or corvettes.
b.) I don't think that's what you had in mind, so let's require to have a ratio between all classes, if you have battleships, you need also cruisers, destroyers and corvettes and have them in a specific ratio. Let's say 1 Battleship, 2 cruisers, 3 destroyers and 4 corvettes. Now the 50 ship fleet has 5 battleships, 10 cruisers, 15 destroyers and 20 corvettes. That looks like a nice fleet. So I bring it to a fight and oh wonder, my opponent has the exact same fleet composition as I do. If we have the exact same technology, then it's pure luck who wins. So how to shift the odds to my favour? Bring another fleet of course, but my opponent does the same. So I bring another, and another. And now we have a doomstack battle. Well maybe not, I may not have enough admirals to do that. But I can still send in smaller fleets. So if I run out, I'll just bring fleets with just 2 battleships and a few extra escorts, they'll come in handy anyway since I'm going to lose most of them anyway. That may be even better than hiring more admirals.
3. Number of fleets with fixed size tied to admiral level and only one fleet without an admiral can use FTL:
Ok, the first two versions were flawed, so let's try a different approach. An admiral can command a certain number of fleets simultaneously but those are of a fixed size. I'm deliberately leaving out the possibility of having system wide boni to their size because that creates unnecessary complications for a very minor benefit. This suffers from the same problems as 2a. and 2b. since basically all that's changed is the scope. Instead of scaling it with larger fleet sizes, you scale it with more fleets.
a.) So to preempt the problem of bringing in multiple fleets without admirals, they can now only move one at a time. Makes sense, players can understand the reason behind that rule, so it's a good rule right? Ok so I still have basically the same fleet as my enemy, how do I bring more ships than he does to make sure I win? I can still use multiple admirals, so I'll just assign all my fleets to admirals and move them together. Don't have enough admirals? Well, I can just reassign them. Problem solved, Doomstack.
b.) Ok what if we limited reassigning admirals somehow, say a fleet must be docked to get an admiral assigned. That sounds reasonable, so I'm on my way half way to my target my admiral dies. Now what? Can't move the fleet together anymore can't reassign an admiral either. So fleet by fleet I bring back my fleets to dock them at a station and assign a new admiral. Well, that's kind of annoying.
c.) If an admiral dies, you can assign a new one. Problem solved! Oh, that admiral is lvl 1, my old one was lvl 5, he can't command the fleet. Ok, if an admiral dies, all fleets he commanded can get an admiral. Problem solved! But what if I can't afford another admiral? I have to abort my campaign because the stupid RNG killed my admiral. No, that can't be, we'll fix that somehow, with
<insert solution here>.
d.) Finally, a solution, now we can get back to war. You can now only bring enough fleets if you have enough admirals. Hmm, the number of admirals I have is exactly the same as my enemy, RNG decides who wins, and there is no way to bring more fleets in. Wait, I can still send individual fleets into the battle, takes a bit longer, but I can bring more ships and win. Both sides do that. And doomstack again.
e.) Ok how about preventing fleets without admirals from taking part in fights, that should fix it right? Every empire has roughly the same leader cap after all, so there is no way to equivalent forces could tip the balance by just bringing in additional fleets. That should work. Oh wait, my enemy is a federation slightly weaker than myself. They could have more admirals, and thus can bring more ships than I can, even though I have more ships in total. Well, that can't be right.
f.) Ok only one admiral on either side can take part in a fight, that should fix it, right? No more doomstacks, yeah! Wait, why am I losing? I have more ships, I should win! Damn with all those extra admirals, they take out all my ships that don't have an admiral.
Ok, I'll stop now. This has gone on long enough. It is a clear demonstration of why you can't fix something by placing rule upon rule to fight the symptom. And that's what the suggestion of capped fleet sizes or number attempt to do. If you make it harder or impossible for the player to reach some sweetspot that let's him win, then the player will either use all the loop holes you create by adding rule after rule and add exceptions to those rules to cover their flaws, to get as close to the sweetspot as he can, or it will create an imbalance. And you'll try to fix those by adding even more rules and exceptions to the rules, to try to balance them. With each rule you add, you make the game more confusing, less fun to play and create opportunities for more bugs. It makes the code increasingly harder to manage and maintain. It makes it more difficult to find a bug if one shows up and it ultimately kills the game because it becomes unplayable.
Making a game is hard work, just as any major software product is the result of hard work. The concept of limited fleet sizes based on admiral levels or what ever else you can come up with is not an inherently bad concept, plenty of games including Paradox games use it in some form or another. But it is not the be-all-end-all-ultimate solution to doomstacks. If a game like Stellaris doesn't have doomstacks, then it is because the developers of that game have found a combination of mechanics, which may or may not include maximum fleet sizes, that makes it so the player doesn't need or want to build them in the first place. Placing restrictions on fleet size does have inherent weaknesses too, just as not having a restriction does, because there is simply no best solution in game design.
TL;DR:
A lot of words to make a simple point. If you want to fix something, then look for the underlying cause first, because trying to fix the symptom will only make it worse. If you have a brain tumor, that gives you headaches, then just eating more and more painkillers will no more help you than chopping off your head will.
@Airowird
Thanks for the support.