Small countries can do that because the people who don’t like you can just flee. Venezuela lost several million in population as they just fled to other countries. So the dictator can remain and rule over people who support him.
That can’t happen in China because no place can absorb even a fraction of their population, so there is no pressure release for the increasingly discontent population.
True. But Mao and Stalin survived in spite of murdering millions and terrible economies. Who is going to oppose Xi? There is no one left.