Huh? A powerful Iran would bring stability to the middle east. Relatively speaking. And Iran and China don't share any borders nor do they share any traumatic history that would fuel present day grievances. Iran and China would be natural partners. So I don't know why you think that China doesn't want a powerful Iran? China's rise is completely different from US hegemony. China has often and loudly called for a multi-polar world where there are several nodes of power as opposed to the US strategy of brooking no peer competitor. Even if China were to become the most powerful country in the world, as millennia of history has shown, China has no desire to dominate and control other countries the way the US is doing even today. Don't be so pessimistic my man.
That is pretty naive thinking especially with China already dealing with its Asian neighbors that hates it already. And you can explain it for us all.