Ming dynasty before it became bigger as the Qing dynasty:
The borders of nations have changed considerably throughout their history. From a 3rd person perspective, there is really no reason to favor the maximum extant of any nation unless one wants to have a nationalistic agenda.
A common mistake is to group all the western countries together as if it was a single entity. There were all separate countries that competed among themselves and each of them becoming stronger. As countries became stronger, they tend to grew their size. So just like how the British have become bigger and bigger, how the Russians have become bigger and bigger, and how the Turks have become bigger and bigger, the Qing has also done so, making themselves bigger and bigger. And just like how the British, Russians, and Turks, have become weaker and "lost" lots of territory, so too the same story of changing borders has happened with the Qing.
Times have changed thanks to modern technology, technology that has not existed in the past 1,000s of years of humankind. Most countries are fine with the status que. The maintenance of the status que ensures China being by far the largest in Asia. I'm not so sure why some people feel the need to want to change the status que to expand China's territory more so. Russia tried that with the Ukraine and now there are a bunch of European military forces ranging from the British, French, and Germans, along with the Americans in other Eastern European countries. That same tendency of wanting to grab more territory exhibited by Russia that China is showing is causing a similar reaction. The more China tries to push its territorial border, the more the surrounding countries will like to see China fall apart. Well I say that knowing that the usual posters laugh at things like "the Quad" or TPP. But it does kind of surprise me giving how long term thinking China is often described to be as. But they fail to notice the trends of US-Japan-Australia-UK-EU-NATO. China is backing itself into a corner with such nationalistic thinking regarding the South China Sea, Taiwan, and Senkaku Islands. These "western nations" probably don't really care so much about Xinjiang and Tibet but will poke about it at best. But I think making some serious efforts towards even Tibet and Xinjiang independence gets put on the table if China tries to make a serious plan of forcible expanding its territory beyond
this under the guise of "China's sovereignty".