Don't get me wrong, I'm talking about a hypothetical scenario here, but clearly somebody who tried something like this would probably think through the ways that they would be able to get everybody on their side, even if reluctantly so.
Well they could do that hypothetically but I still don't get why would China of all countries would want to do that!
You say it would "rattle the entire world economy" but I don't think so. Even if Bitcoin died today, it will only affect a small portion of the global population that has adopted Bitcoin (5%-10%).
What else would they gain if they had control of Bitcoin? A centralized and censored payment system in that hypothetical scenario.
Well they already have one that is pretty successful called Digital Yuan and last I checked its adoption was going fine and had already processed trillions of Yuan worth of transactions. And that only costs them a teeny tiny fraction of what it would cost them to actually mine bitcoin at large.