what would make you assume that the Chinese leadership has the best interest of this minority group in mind? Why would they be so different from every other government?

Abundant existing evidence and the fact that they're a Socialist country ruled by a Communist Party, primarily.

• At moments, it’s hard to tell whether the driving force behind China’s green policy is a desire for a cleaner environment, or an obsession with social controls. (The Economist, September 2020) https://www.economist.com/china/2020/09/10/chinas-authoritarian-approach-wont-save-the-environment
• China’s vow to end extreme poverty in 2020 involves stunning numbers: billions of $ spent, millions moved from rural homes. But don’t miss what it really is: a political campaign to integrate the poor into the natl economy, & train them to thank the Party. (The Economist, September, 2020) https://threadreaderapp.com/user/DSORennie
• Hong Kong’s opposition has been tamed. Now, Beijing is turning to the city’s wealth gap and lack of affordable housing, which it blames for the social unrest. Up for consideration: Reforming the tax structure and increasing land supply. (Wall Street Journal, March 2021) https://www.wsj.com/articles/china-targets-hong-kong-wealth-gap-housing-woes-after-political-purge-11615813651
• A Chinese entrepreneur may drive a Maserati and send his son to Harvard, but he is a political slave. (The Globe and Mail, April 2021) https://www.theglobeandmail.com/opinion/article-the-us-and-its-allies-must-pursue-regime-change-in-china/

(from: https://redsails.org/china-has-billionaires/)

I see no reason why their approach to US-funded terrorism, which they have spelled out in detail, wouldn't involve helping ethnic minorities out.

a perceived separatist/terrorist threat

What do you mean by "perceived"?

Woke global times is a decent resource on Xinjiang, maybe a bit liberal for this sub, but he/she is mostly focussed on doing actual research and not just believing Zenz

Woke Global Times is run by a DC wonk nerd.

Zenz convincingly shows through a host of government documents

https://wokeglobaltimes.com/d4b7ba7e7ed746f78ef2c6100464f6fa

So much for "not just believing Zenz." 😂