These are just projections of Western white supremacist ideas on China. It is true that the ruling elite of China wasn't Han for half of the last millennium but that is irrelevant because nations, as we know them today, didn't exist back then. The idea of nations is mostly a modern idea. It is so global and fundamental which leads people to think it always existed but that is simply not true. The said Mongol ruling elite used to sell their tribal slaves to Han and Arab landlords to finance their luxurious lifestyles. Over time this led to Mongols becoming the lowest caste of Yuan Empire unless they were nobles. Most of the Yuan army that conquered China was Han and there were a lot of Mongols in uprisings against the Yuan Dynasty. As I said, never think about nations while reading about pre-1700s history. The concept didn't exist. There were just ruling factions and their lands. Qing and Yuan Dynasties played the political game well and they found a lot of supporters, which included a lot of Hans as the demographics of East Asia would mandate. That enabled them to rule lands that we today know as China.
And if we are talking about modern times, the term "Chinese" includes all ethnicities living in China, a gift to China by the Qing Dynasty. Both ROC and PRC wisely adopted the same policy too.
You know that's interesting. This brings me a lot of old memorys,decades ago when Chinese internet was pretty free compare to now,there were many ethnic minority forums.
I had visit many of those forums,the atmosphere was very toxic and antagonistic against Han people and China in general. There was nothing explicit against the CCP nor anything about "independent from China",I guess it's just that the server is located inside China and they don't want the forum get shutdown by the authority. But the anti-China sentiment is very clear on these forums,it's filled with negative news about China,you‘d get banned if you say anything good about China.
Specifically,there was ethnic Zhuang/Miao forum,who relate themself to Southeast Asia countries rather than China. And I remember some Han poster post something like “we are all descendants of Yan[di] and Huang[di]炎黄子孙 ”,then got reply like "No,we are the descendants of 蚩尤Chiyou,we are not the same with you(Han)".
And there was ethnic Korean forum,who relate themself to North and South Korea but not China. They claim that Korean war was mainly fought between North Korean and US army,Chinese army had no role in it,and China somehow is blamable for the split up of two Koreas.
Then there was ethnic Manchu forum,it's just full of horseshit like how great the Qing was and Han people are ungrateful.
There were more,but it's been 10 years and I forgot alot.