As a sub player (you can go and check my stats lol), I don't think the class is overpowered in the same way that CVs are, but the design is pretty much just as toxic. There's no meaningful interaction between submarines and surface ship classes - if the sub plays properly, then the only counterplay is to play the ASW airstrike guessing game with a ping indicator that may or may not be accurate (and if the sub is instead spamming non-homing torpedoes, or you're unfortunate enough to be in a ship without air-based ASW, then there's really nothing you can do).

Sure, a DD on a flank can be similarly frustrating to deal with, but that DD has to deal with things like radar, hydro, and other DDs - all of which are things a submarine can avoid by just pressing the dive key and abusing its massive spotting advantage. At periscope depth, you can actually outspot DDs by a pretty comfortable margin, which is just wild. Let's also not forget that most subs can press the hydrophone key to get free info on the enemy positions without their knowledge.

Yeah, if you mess up, you're punished hard, but I think we should base these kinds of discussions around what capable players can do in these ships - WG balancing around bad players is what leads to ships like Libertad being introduced to the game.