> There is no right or wrong
There's such a thing as too much moralism in geopolitics. There's also such thing as too little.
Geopolitics is amoral. "Moral" is only brought to build a narrative, ie. for propaganda.
> They are disrupting the Western-established order.
Yes, this is the problem. That Western-established order sees a full third of global maritime shipping transiting the South China Sea.
> The most strategically impacted countries are actually the East Asian ones, Taiwan, Korea, Japan. That's an important point because they are almost de facto US protectorates on mainland China's doorsteps.
Speaking of rhetoric.
> There is no right or wrong.
No, there is very much a right and a hypothetical wrong here. Right is for both the sovereign territory of nations and international waters to be respected as such. Wrong would be for the PRC to be able to assert its most extremist position on what parts of the South China Sea it considers to be its territory as this line cuts through both the sovereign waters of other nations nearby and their land in some cases, allowing the PRC to put its thumb on the scale in one of the largest shipping channels in the world. Don’t forget, the State called the “People’s Republic of China” is by its own laws only an entity subordinate to the Communist Party of China. No country should have that much power over international shipping, but a totalitarian one even less so.
> both the sovereign waters of other nations nearby and their land in some cases
I would refer to my previous comment about what happened in the past two centuries. What is "sovereign water and land" depends on past agreements and use of force. In this case it is not even always clear because indeed most of the area is disputed.
What power a country should or should not have is relative to which side you're standing. The US have military control over the Panama Canal, should they have that much power? So far China has less that 1/10th of the power the US have on the international stage but it is growing. It is 'bad' if you are the US, it is 'good' if you are China.
Now, the political system in China is a red herring and irrelevant. It's only convenient for the US as it allows to build an anti-China narrative more easily ("freedom!"). But if China was a democracy nothing would change in the South China Sea or with respects to the issue the US have with China, which is that it is big and powerful and does not defer to them.