Why won't the Chinese system just collapse eventually? You have a small elite who perhaps currently are well-selected (besides the point) but what is preventing that elite from leaving the reins to someone who is not so good? With the added effect that the incompetent ruler will call upon the reputation for competence built up by previous rulers?

Seems like it's just cultural norms all the way down. If people want to take advantage of the system, they can break these norms while pretending to be what they used to be.