My theory is that Russia threw their D league to go fight so that no one could accuse them of them actually trying to take over.
I don't know about China, but Russian exports are mostly soviet-era models, and they are known to have huge maintenance issues. Also note this: in the USSR they knew how to build things, but modern Russia can't. We have no electronics industry, no machine industry, we can't really make commercial airplanes, and we can't build a decent car. How would country with such capabilities make state of the art military equipment?!
I'd rather trust my national security on equipment that's subpar but reliable and predictable, instead of trying to make my own and failing. Kind of like home security: I'd rather buy a lock for my front door that may be not perfect rather than trying to machine my own better version, even if I technically know how it works and could maybe make a working prototype. Military development is really, really expensive and extremely hard to do right when your state is still developing and running low on qualified engineers, physicists and mathematicians.
In any case, having recent russian weapons is more than enough when your neighbours are equipped with leftovers from the fifties.