There's no point talking about USA's theoretical capabilities to end a war quickly if they can't use those capabilities to end a war quickly. Yes, the USA is holding back on invasion, carpet bombing, total war and nukes. It doesn't matter to the Chinese assessment for the capability of sustained high intensity US military operations.
They’re different leagues, and in a gloves off war being on the receiving end of the US military would be devastating.
I think if China makes a move it’s because they perceive US political will to defend Taiwan to be weak enough that there won’t be a real protracted fight or escalation.
Which I half wonder if that is why they aren’t more defensive about Iran. Bleed out the political will of the US populace on a war and it’s unlikely we’ll want to support another one anytime soon.
Then the Gulf oil infrastructure would be gone in retaliation and the impacts to the global economy would be severe. Trump's popularity and legacy would be utterly destroyed.