Cid, what we mean when we say ASW is too effective is that subs go glug glug glug in the game and that is about all they do. Setup in a game optimal fashion, air assets can clobber subs. And the ASW task forces in the game make Johnny Walker's efforts look like baby steps.
Also, air/naval coordination is just not in the engine - we're told this was never intended to be a tactical game.
To start at the end - tell em (loudly and repeatedly until they get it) that this is NOT a tactical issue - you cannot simulate operational effects if they are not present. Even a SINGLE plane matters - and you simply cannot simulate protecting a TF if it does not get in the code.
To go back to the beginning - in my experience subs are either effective (for me) or irritating (if enemy). I do not like the lack of sub operating mode options - and I agree that being forced to attack when you just want information - or being forced to attack on the surface when you would not - or being forced to move on the surface when your would not - all increase attrition over reality. But I find even the AI can use subs in ways that are not nice - and I can get much better scores than history with them. One player said that I use Japanese fleet boats like modern SSNs!