If the Chinese side has access to hypersonics, what makes the US unable to procure them? They've just recently completed 2 successful test so having b-2 launched hypersonics is not out of the question. If hypersonics are at play and they are extremely difficult to intercept, it's not a stretch that the US will priorities hitting critical chip making infrastructure over the long term seeing as those hi-tech factories are extremely fragile. Over the long term they don't need to beat China in the first Island chain, just make it so that China will seriously struggle to push past, which they will through targeting those critical supply chains. They could also technically target nuclear powerplants, but that's a road that leads to MAD, so it's kind pointless to speculate.
We've seen that volume of fire alone is not enough to win wars from the Korean war to Vietnam, so what makes you think that local fire superiority will allow China to completely suppress Korea/Japan war making capabilities? If invading Taiwan required an operation greater than D-day how will China ever manage to stop Japan from lobbing missiles back?
Even if US could hypothetically overcome the tech hurdle for hypersonics, such missiles would be insanely expensive and therefore unsuited to strategic bombing. For the same reason Russia doesn't simply shoot every ammo depot in Ukraine at once using Zircon and then roll in unopposed.
Producing tons of lower grade missiles etc is not difficult, especially since China would ramp up military spending to probably 5% at least in order to exceed USA a few years before war. Stuff like J-20s to some extent needs to be completed in special facilities which would still be well hidden, but a CJ-10 could feasibly be made in any major industrial park.
Taiwan Island is surrounded by defensive installations, if US wants to invade, they need to win a decisive battle over practically the entire PLAN and PLAAF while fighting in an area where they're completely exposed.
The situation facing US and any country unfortunate enough to join the war on their side would be similar to Imperial Japan in ww2. Without raw resources, consumer goods from China and it's allies, the attackers would be fighting a timer towards economical collapse, while PRC gains in strength the longer the war lasts.
As for how South Korea and Japan would be suppressed if they join, Korea would be the first to go, because its so close to China, it can be blockaded far more easily than Japan, and since the Ground Force wouldn't be fighting aside from defending Taiwan Island, the SK army will find itself staring down not just the entire NK and large parts of RU Army, but the brunt of the PLA as well.
Even with full control over mainland Asia, the invasion of the home islands and Okinawa would still be an immense feat requiring huge logistics investments, extensive coordination with Russia from the sakhalin front and is inherently a huge risk. It would be larger than Operation Overlord in scope.
But China has quite a bit of prep time, and what stacks things in their advantage is that the Japanese economy will be completely wrecked by energy sanctions, blockade and air raids.
