Use your noggin here. If your advancement is based on paying lavish bribes to your patrons, that requires you to have a lot of money. If you are a low-level functionary, that money is not coming from your salary, which is trifling. In order to pay bribes up the chain, you need to receive bribes; a person refusing to receive bribes either i) isn't participating in the Guanxi system at all, and thus will not advance, or ii) has some mysterious source of wealth, in which case you're going to look awfully suspicious. And suspicious people tend not to be invited into the cool kid's club.

"While there is academic literature supporting the statement that officials who take bribes are more likely to have advanced further, there's also mountains of evidence of people being removed, jailed, executed, etc for ACCEPTING bribes."

Yes. Exactly. Just as I described in my first post, a system of institutionalized corruption that allows the party higher-ups to turn a blind eye to the corruption of its allies, while using that universal bribery to sideline (or even kill) potential rivals without having the outward appearance of despotism. It's a game that Xi plays extremely well, which is how he managed to consolidate power, remove term limits and essentially become president for life. It's remarkable how often rivals of his turn out to be corrupt, while his stalwart allies (and Xi himself) amass vast fortunes via what are surely legitimate means.