Except the purpose isn't social mobility for most Chinese people. Remember the '躺平' 'lie flat' propaganda movement the west loved talking about a few years ago? Yeah that wasn't new, or temporary, nor did it ever go away (and no it's not illegal). That's just how most Chinese people have been seeing life after getting up to 'western' standards (I would argue a roof, consistent meals, cheap electronics, and free healthcare is closer to the western standard than not, and that covers ~900 million people.) Yes there is a rising upper middle and upper class, but also the living standards of the bottom 50% are better than more than 150 countries and that's rising just about as quickly.
These facts skew the traditional western reporting of economic health, because western economists assume everyone wants to grow infinitely, and that's just not the case.