The USN is going to keep being aggressive in the SCS until the amount of deployed PLAN submarines (which is already substantial) becomes overwhelming. Over the next decade or so, you're going to see the USN decrease their FON exercises in the SCS and there's going to be a clear stand-off distance the USN is going to maintain for security purposes.
FoNs don't depend on factual vulnerability, it's a peacetime customary law practice. Ships did and continue to do it in areas where they aren't survivable in wartime. At best, it's done under implication that this particular ship may be sunk, but country behind it is stronger than you(skillful attachment of F-47 here, totally not off top! jk, see below).
Though even that is debatable: for example, famous British fonops through Crimean waters, done on simple strength of will, without much strength behind it; should Russia try variant of
Corfu back then, it would be a disaster. But UK carefully gauged opponent's will, and as a result BSF was humbled for free.
PLAN can deploy overwhelming number of subs to SCS right now (and can for 2 decades, since they got enough kilos) - it just isn't that worthwhile (after some point of saturation it'll just make ASW easier).
That changes now is mass production of sufficiently competitive nukes, which stretch non-ssk capabilities far beyond.
That keeps FoNops viable is ability of USAF, USN and USMC to contest and ideally contain China's potential expansion (with goal to roll it back in).
Where USMC is more about contesting(F-35B is good enough for that), but new USAF and USN aircraft (as well as their ground investments) - stopping and containing (F-35s aren't good enough for that by themselves on theater, it's a high end fight).
USN surface units aren't in SCS wartime picture, they're just not survivable there. They are supportive assets, unless sides attempt to move battle space geography(i.e.conduct offensive amphibious operations).
What matters overall is strike bandwidth(i.e. rate of damage, materially affecting frontline forces, as measured against force regeneration rate and it's sustainability), provided by survivable strike fighters(more) and stand off munitions (less, they're quite expensive and production limited - per volume of explosives delivered).
Core capability itself, thus, is F-35A (and maybe land-based F-35C).
Moderator of this capability over neutral/hostile airspace is land-based air superiority aircraft.
I.e. J-20, F-22 and F-47.