Technology

Yes...but what if you had like...a lot of them. /s

Joking, but it does seem China is heavily invested in building submarines specifically. I was curious if they had a doctrine against American naval power involving submarines. Despite what you said, I'd imagine submarines can carry a sizable missile platform and strike from far, far longer distances now. Striking convoys, trade-routes, etc in order to cut off supply to the "huge fleet". Of course they'd be protected but even the best equipment like you mentioned doesn't always stop 15 missiles from all different directions going at mach jesus. Houthi's managed it while on land.