Two things I wanted to say.
First, when China was dominated by one single party, you can see that as strength but you can also see that as weakness. Why? If you look at Chinese history, what followed Han and Tang Dynasty? That Three Kingdom (after Han) and 5 Dynasties 10 Kingdoms )(After Tang). There are probably only 2 times in the entire Chinese history before modern China when a consolidated China handed power (albeit violently) another consolidated power. That's from 秦 (Qin Dynasty) which arguably the first time China proper being unified and from 隋 (Sui Dynasty) which only last for 30 years or something like that. And then you are talking about anything post Yuan Dynasty
The most "stable" period is always followed by the most "unstable" period. The reason being so is the monarchy system where 1 man (usually a man, except for "武則天") rule the entire country, first, it is very susceptible to the opinion on the people around the king, second, it's like trying to Band-Aid a country by yourself, you just can't do it if and when everything start falling apart. Unlike European Monarchy, the King governs the kingdom, but then there are things like Privy Council that advice the King.
Which mean, the problem for Europe, especially in WW2, is not stemming from their own governance, but rather the greed/motivation of others. On the other hand, the dynasties in China always followed an explosive with an implosion. That's the different here.
My second point is, nothing last forever, would US still be dominated in 50 years' time? I don't know, but then the issue here is, if it wasn't, that could not be because some country in the global south don't like the US, that can only be either a better country emerge and replace the US with a better portfolio, or another World War that devastated the world and redrawing the world order, that is the way it can only happened. Simply because the rule based order is strong, while you may or may not like the American foreign policy, you still need to deal with America, and if you have any problem with it, you are not just going to see the big stick of America, but rather a coalition of countries who are going to do the American bidding because it wanted to stay on the good side of the world order.