IIRC (I'm just an occasional observer), this system broke down with Hu Jintao, Jingping's predecessor. Both men held all three senior positions concurrently. Jintao didn't have the clout to hold onto the reigns, but it's unsurprising that Xi Jingping has done so.
In any event, my point is that until recently it was impossible for any singular political figure to have as much political or social influence as Xi Jingping. Xi Jingping's rise to power is the result of what is effectively a constitutional shift (regression?) in the structure of political power in China.
Hu didn't start holding all three senior offices together. His predecessor, Jiang, did. Not that it matters anyways - China's paramount leader before Jiang, Deng, was neither head of state (President), nor head of government (Premier), nor head of party (General Secretary).
Hu is generally considered not to be power hungry. He is well-known for collective leadership (by the Politburo Standing Committee where he is the top ranking member) and is praised for stepping down from all positions voluntarily at the end of his term (Jiang kept his position as the head of military well into Hu's term)
The rule was only on the paper. Prior to Jiang, all intermediary period leaders were forcefully removed from the office. Jiang almost managed to stay in power indefinitely, just like Xi. Hu was purposefully undermined, and politically eunuchised from the start by much stronger parties who ran the CPC behind his backs: namely the gang to whom Xi is the heir to the throne, and Jiang Zemin's one who also wanted to put their own man there. Were Hu having even a sliver of political power on the level of Jiang, or Xi, he would've tried to stay the third term too.
Really, there were really no rules in Chinese political system besides the survival of the fittest (or the most ruthless.)