For today´s standarts? yes. For THAT particular period of time? No.
Which is the question I made in my first comment in this thread: How has the doomstack problem been solved?
The proposed solution will result in exactly what we have right now, but with the extra hassle (clicks) to assemble extra fleets
You realize that the point is that, if an ancient admiral can command hundreds of vessels using primitve means, a futuristic admiral using futuristic means can do the same, right?
You also realize that the "smaller forces in those examples" had several dozens to a about a hundred and half vessels under the command of an admiral, right?
I'm not sure if someone else has pointed this out yet, but the real limit of what is possible to command in any kind of space combat has absolutely nothing to do with the capabilities of the admiral in question but the capabilities of the computers available. This is due to the distances involved. Ancient admirals did not need to deal with effectively infinite battle space and the difficulties of possible enemy positions spiraling into being completely unpredictable as time goes on. At space distances, even minor maneuvering of any of the ships involved at a large distance exponentially increases the difficulty of acquiring a firing solution, and that's without taking into affect any possible countermeasures that might exist (Such as physical CM like generating an expanding radiation cloud due to high energy particles firing through stellar gas, or electronic counter measures like bombarding incoming missiles/torpedos with fake positions of involved ships to confuse targeting sensors). The amount of factors that would need to be calculated simply to fire one weapon from one allied ship against a single enemy ship is astronomical, and even if we had instant communication of some kind eventually you would reach a point where every additional ship you add that has to be coordinated in the fleet wouldn't increase the capability of the fleet by the expected amount due to increasing the complexity of the calculations. And that's assuming that you have instant communications. If you had to deal with orders being given at the speed of light then in a large fleet you would likely be looking at minute or more delays to every order reaching the ends of the fleet further complicating any kind of calculations of enemy positions as you have to predict where they will be at that particular moment. You can just handwave it and say that the computers are perfect and can do it no problem but that's equally as arbitrary as saying that they can't and that there's a limit to what can feasibly be coordinated in each individual fleet.
As for how the firing speed increase doesn't make sense from a realistic or immersion perspective, I'm thinking about it like this. Any form of space targeting is all about probabilities. There is no 100% exact targeting unless your weapon hits instantly regardless of distance, your sensors give instant information of enemy positions, that information is processed and coordinated with allied ships instantly, and is sent to your weapons instantly. In a situation where the enemy has, lets say, double the ships in the same arbitrary amount of space that you do, it could feasibly be faster for each of your weapons to target due to them having the possibility of calculating a solution that has high probabilities of hitting one out of several enemy ships. And if you say that the fire rate of a weapon is based significantly on the time it takes to acquire a firing solution, then it makes sense of a kind. Does it make perfect sense? No, but it's good enough for me.
As for how this update deals with doomstacks, I think it remains to be seen. If there is a system in place where you are unable to effectively use ships if you cannot pay for or supply them, then using small fleets to cripple enemy economy while bolstering yours could be an effective strategy to deal with a doomstack. And if starbases are a main way of gaining fleet capacity then going on a rampage capturing smaller, less important systems could very well create a situation where you force the other empire over fleet capacity and bankrupt them even if they have just doomstacked more important systems. The main idea I think is not to totally remove having one large fleet (Now likely composed of several smaller fleets following), but making it so that there are other viable strategies to fighting wars. If you opponent has one key choke point system with their entire fleet in it and a huge starbase to defend, of course you're going to have to bunch your whole fleet and send it in (Assuming you don't have jump drives). It would never work for them to create a situation where you can't shove your whole fleet in a system because it would be completely unrealistic given the actual size of a solar system. They're not really trying to make doomstacks worse just make other ways to fight viable as well. We'll see how well this strategy works, and it certainly might not be as effective as they want it too, but I'm excited to see what they come up with.