China outnumbers the US population 3:1. Do you remember the last war the US was in where our battlefield casualty conversion was anywhere near as low as 3:1? Me neither.
The Chinese outnumber us, but they don't outnumber us enough to compensate for a mediocre military.
Do they have a mediocre military? I don't know how good their military is one way or another actually, aside from the fact that they certainly got a lot of stuff from us during the Clinton years. Maybe they ain't so mediocre anymore.