so I don't think the in-game time is the real issue.
Well, I have time, because I design my tank before the game.
knowing the design and doing all the clicks are two different things. in peacetime it's not that big a deal, though in 1 hour to Danzig modded speed 4 it can get tricky sometimes. but when you're Germany or the USSR, it does get very stressful doing all the clicks once you're at war, even if you have a coop. far more stressful and "difficult" than swapping fighter 2s to pre-BBA upgraded fighter 3s, for example
At the start they were a bit OP, but when they got nerfed a few patches after MTG they were totally able to be countered. But rather than taking the time to understand how to counter Sub 3's; most host's kept the ban on them
some more casual servers may have kept bans because the counter isn't super intuitive players and they had too many games ruined because otherwise competent new UKs weren't really ready for it, but competitive ones didn't ban it because people with thousands of hours "didn't take the time" to understand how to counter sub 3s, they banned them because they were ridiculously cost-effective and because they forced you to massively overbuild convoys so that in the first few months, before you'd killed the subs off, you wouldn't just run out of convoys and fuel and die.
it's not that they're "uncounterable" in that they're hard to kill, but in that it will always cost you far more to kill them then it costs them to make them.
Most of the spam tactics like strat bomber spam have a counter, however that requires a bit of planning to do, so most people just get frustrated.
wrong again. even with harsh rules against flicker bombing, as long as you have yellow air the bomber always gets through. and once you've deleted their airbases and civilian industry then they won't even have yellow air.
Sense he has gone for a lot of light attack CA's; he's not going to have enough screens. My subs will then kill him bit by bit.
maybe the issue here is that you haven't played with good enough people who know how to fully milk sub3s and strats. if someone doesn't have enough screens, regardless of navy build, that's a hard skill issue on their part. and if he/his AC doesn't know how to put out tacs over the seazone by the port that's even more true.