When I left the world of ASW fifteen years ago, the Russians were building (thanks to the Walker spy family)some fine submarines. For the chicoms we aren't talking about dominance. All they need to do is deny the US Navy free movement in the waters east of Taiwan. A fleet of even old Kilo diesel/electric boats will keep aircraft carrier captains awake at night.
I've read about the damage done by the Walker clan and Toshiba.