He has no more mandate to lead China than me, a random dude in China. He's not elected, he didnt perform incredible national deed (like some victorious war general sometimes), he's not pushed by the people etc.

It feels he's there because he fits a role set by a small minority and will perpetuate the party he likes rather than help the country or represent the people. He's possibly legitimate to lead the communist party however. Just not China.

For instance, a legitimate leader encourages competition, transfers power to successors, accepts counter power, is benevolent to critics, works on compromises rather than absolutes etc. And if he doesn't, the people get rid of him ASAP. You get legitimity once there's someone judging it. I can't perceive who's above Xi, and it's certainly not us, the taxpayers.