From my opinion U-Boat War is currently not what it should be:
intelligence war.
U-Boats never attacked in fleet encounters, even the shoot of Prien was just an single event, planned by Dönitz himself.
U-Boats where slow moving fragile nut shells, they only have to shoot at convoys. I think just because of a few lucky shots at capitals we dont need any sea attack at all on a sub.
Subs were only a close second to carriers in terms of sinking capitals throughout the entire war. 8 CVs were sunk by subs, compared to 9 by aircraft (land and carrier), and 1 by BB; and I know there were at least 3 English BBs sunk by U-boats as well. A bunch of escort carriers too. That might be a few lucky shots, but that's still an entire navy's worth of capital ships they put on the bottom.
The Reality was that U-Boats where nearly invisible to fleets just cruising arround. In Late War only the Radar where a big issue for them.
That is why the early years of war where called "the happy times" for U-Boats.
By ~1944, British ASW had improved to the point where German subs were making massive detours just to avoid detection by British destroyers and planes; and focusing most of their efforts on surviving, with actually sinking anything a very distant second. There were a number of techs involved (hedgehogs, leigh lights etc), there was the codebreaking, and a big part was just the brits getting their acts together doctrinally.
The other big threat to U-Boats are Planes. A Plane is much much more dangerous to an U-Boat as any DD can be. The only thing a U-Boat can do against Planes is dive really really fast. Just a single hit from the Gun of a Plane into the Hull and a U-Boat cant dive anymore. And then the Bombs of course, directly at the top of a sub. As in Real Life, the main Sub Killer where Planes. In Early War land based, later based on Escort Carriers.
I don't know about American and Japanese subs, but 264 U-boats were sunk by ships, 250 by planes (at sea). If anything, relatively more were sunk by ship in 1945 than 1943 (and planes weren't really terribly effective vs subs until the invention of the leigh light anyway).
And then we can talk about the impact of submarine warfare to the industry...
The other thing about effects on industry is that, sure, the German U-boat war failed in its objective of strangling British supply, but the American submarines absolutely decimated the Japanese merchant marine and were probably equally if not more instrumental than the carriers in winning the Pacific War. They were really good.
i thought the patch was going to reduce cost of subs and make them more effective against convoys not the extact opposite. add in increased sea attack and i'm really confused
Convoys are much more expensive now and subs are a bit cheaper so it should even out to be a significant net plus for subs.
The increased sea attack mirrors the historical effectiveness of subs against large warships caught at the right time.