The USSR famously subsidized and gave autonomy to the non Russian SSRs. Russofication was obviously a problem but much less of a problem than during the monarchy or the post union capitalist state. There is a reason why the non Russian SSRs voted at higher rates than the Russian SSR to stay in the USSR during the referendum before the illegitimate dissolution of the soviet union.
https://www.marxists.org/reference/archive/stalin/works/1920/11/13.htm
China famously exempted all ethnic minorities from the one child policy.
I would read an English translation of "On the Governance of China" as well as this https://redsails.org/china-has-billionaires/
Even Lenin acknowledged that you can't get rid of capitalism quickly, and China started from an even worse position than the USSR.
Empires competing and creating multipolarity benefits China, other socialist nations, and the imperial periphery looking to break free. Keep in mind that mao's three worlds theory is a major influence on some socialist factions in China, even if it is reductionist. Russia maintaining strength to challenge the US(including if it comes through a defeat or truce in ukraine)(note that China is pushing for a truce which would maintain Russia's ability to defend itself from NATO better, but supplying them to maintain their strength) is a good thing in their calculus, and I haven't seen any compelling rebuttals to it.