It's Western arrogance to assume that the Chinese give a rip about international diplomatic points or not.

No one cares what the Chinese think.

Before the U.S. gets into a proxy shooting war with Iranian clients in the Middle East (if that's where we end up), our allies want to know that we've at least explored every easy option to resolve it diplomatically. And that they have cover with their electorate so that none of their political opposition can come in and say that they (or their American allies) missed an opportunity to solve this diplomatically.

You check the box. It may indeed be a vanishingly small chance that Chia will pick up the phone and tell Tehran to knock it off, or even tell them to talk to the Americans. But you have to make the trivial effort to at least ask China to do it, and then repeat the ask in public when it fails, so that you've done your due diligence before considering other options.

That's basic statecraft, not incompetence. Of course they're likely to tell you to pound sand. But you don't assume it, and not even bother to check.