I don't have good source on Chinese demography, picking info about it one line at a time.

Anyway, there's no reason to think that Germans would easily defeat post-Imperial Russian Republic (given no Bolsheviks and therefore no civil wars, no mass emigration, famines or murders). Soviets basically lost half of pre-WWII years on chaos.

Russia without Soviets would look more like 350M strong Norway than like 140M strong Nigeria how it ended up.