Your theory is just the economic version of "democracy don't fight democracy", whereas if China become democratic, all the animosity would evaporate overnight, which is far from the truth. Just by the virtual of its economic size, the conflict of interest between the US & China will be unavoidable, and while unlike Japan, US cannot order China to yield to its dictation.
If China and the US can come to an agreement about how the world order should be structured (whether China is a democracy or not), then the tensions will dissipate. The size of China's economy isn't relevant, just as it isn't relevant in discussions between the EU and US, the two largest economic blocs. That's because we (the US and EU) have a generally compatible view of how trade and law should be structured.
I would not be so quick to dismiss the possibility that our (China's and America's) views will converge--history has shown that straight-line extrapolations of the future are a fool's game: before WWII, we were friends. Then we were enemies. Then Nixon went to China, and we were friends again. And now it appears we are becoming enemies again. Do you have the confidence to predict what will happen in the next 30 years, given this cycle? If so, why are you so confident?
As an aside, the reason why the US has such leverage over Japan is because Japan fears China, and will make large concessions to the US in order to ensure American protection. The most incompetent part of the CCP has been its foreign policy, making enemies of most of its neighbors. Had the CCP continued its gradualist approach, the world order would have naturally transitioned to China (just as it did from the British Empire to the US). The CCP (or is it just Xi?) got impatient and reached for glory at the expense of the other Asian countries, and now the US is probably more popular in Asia than we've ever been.
Australia's (and increasingly, the UK's) close relationship with China demonstrate that this does not have to be an East-West issue. Indeed, Japan has long been one of China's largest investors, and the DPJ was overtly pro-China and anti-US, but the CCP screwed up with its Diaoyu nonsense, and now Japan is moving back to the US and re-arming as well.
My point: China controls its own destiny, and if it wants to create hostilities, it can continue to blunder in the SCS and ECS. If it wants a peaceful transition, resulting in its own supremacy, it can return to the "peaceful rise." Nothing is determined, and conflict is not inevitable. But it's up to China to decide, not us. What changed in the region was China's policy, not ours.