Radar should increase the gun hit profile not damage, so that the hit chance stays the same later in the game. Right now the hit chance drops because ships get faster.
This is a tricky one, because each in-game tick is an hour, so each 'tick' in a naval battle (even taking into account that an hour in a naval battle isn't the same as an hour in the actual game, from a simulation point of view) represents a lot more than one shot (so an increased hit chance would mean more damage over time). That said, I have sympathy with your view here, and don't think it's a bad idea in principle
(I'd want to test it before having a view in practice).
CV free shotting time should be moddable (separate from sub stuff)
One of the big issues here is that patrol fleet engagement time is counted in the CV free shooting period - so if a patrol fleet finds a task force with a CV and engages them (which they often do, even when their rules of engagement suggest they shouldn't), and then the strike force for that patrol fleet shows up 32 hours later, that late-arriving strike force doesn't get any free-shotting time (and I've tested this - the late-arriving Strikeforce is vulnerable to enemy gunfire from the get-go). I like the free-shotting idea in principle. but at the moment the way it's implemented has too many edge-cases that lead to wonky results.
I do like the idea of fleshing it out a bit more, which is what you're suggesting, so it's possible to get more historically plausible results
But let`s lay it out in terms of ingame techs:
Battleship wize, Bismark is equivalent to 1920s design, give or take, due to 2 gun turrets and 380mm calibre.
In DDs/CLs Germany didnt deploy any models above 1936 tech in game, as far as I undestand, maybe 1940 DD.
Carriers - Zeppelin was not top notch design.
So, in game, Germany invested in ~350-450 research days into naval hardware, if we take all subs techs. There is around 900-1300 extra research-days that can be taken in naval tech tree, and I would assume US and Britain each invested over 1000 days into naval hardware tree, Japan probably a bit less, at 800-ish for poor ASW.
Germany also needs to invest 192*5=1000k base research days into subs doctrines, and can cut those by naval xp and discounts further. Since their surface navy was neither large nor successful, besides the lucky shot on Hood, so I`d say no further doctrine researched.
GB, US and Japan, on the other hand invested 2-3k research days into their naval doctrine, So, IMO, Germany "neglected" their navy by ~2k research days(500-700 in hardware and 1-2k in doctrines), compared to big 3 navals.
If we're talking in-game, the devil is in the detail, and Germany actually researched a fair bit of naval tech. My 'off the top of my head' take is:
Bismarck's armour scheme may have been late-WW1 era, but her engines and actual armour weren't, so I'd say that her BB tech is at least 1936, and the engine 1940 (and the engine is part of the hull tech). Her secondary guns were also the second, not first gun option, and she had radar and better-than-base fire control. I can't recall off the top of my head how many techs she doesn't start with from that, but it's at least a few.
Further, Germany laid down a successor class to Bismarck, for which they'd developed the hull and gun design for, so historically she researched 1940 BB tech, even if industrial limitations meant she focussed elsewhere in terms of what she actually built.
Cruisers are similar - the Hippers were solid 1936 models with at least the first cruiser gun tech, second-tier secondaries, and at least second-tier cruiser armour (noting that the way the armour works in the tech tree makes it almost impossible to match to historical designs, so this may or may not be practical). The M Class cruisers (three laid down, but not completed) arguably were to have 1940 propulsion).
You're not wrong about Graf Zeppelin, but Germany did develop carrier-capable aircraft to fly from it, so there's more tech used up to support her navy.
In terms of destroyers, she definitely started building 1940-era DDs (iirc with dual-purpose main armament, although that might be design only - I can look up if necessary, it's just a lazy Sunday morning here, and I'm keeping it lazy
), and her DD machinery was advanced, if not entirely reliable, so she definitely got to 1940 DD tech.
With the subs and the torpedoes (torpedo buffs, not tubes) she researched the lot, and Germany was one of the leaders in mine warfare as well, so to get her historical tech, she needs pretty much all the mine techs other than aerial minesweeping (and I can't say beyond a shadow of a doubt that she didn't have that, but I can't recall that she did).
Then, with doctrines, it's important to note that historically Germany didn't (by any means) just develop doctrine techs and forget the rest. Applying the in-game doctrine trees to historical naval doctrine is very difficult, but as well as the entire sub path, I'd think she would have historically 'researched' (doctrine is more developed than researched, but given we're talking in-game) all of the non-carrier surface techs, as well as at least half of the convoy defence techs (while Germany has very few convoys to protect in-game, this is due in no small part to the millions of tons of shipping that travelled in coastal convoys not making it into HoI4 - historically, Germany had to spend no small amount of effort on commerce defence).
