It might be worth bearing in mind that the Soviet Union got absolutely humiliated by the Winter War against Finland, much like the Ruskies are in Ukraine. However, a few years later they steamrolled Nazi Germany when they were properly equipped and motivated (by the western allies).
Who is to say that China wouldn’t be willing to lend-lease them equipment to fight a proxy war against the west? China’s industrial capacity is already, like the US in the 1940s, the highest in the world.
In the event of an attempt to do so, the US would cut China's sea-borne oil pipeline from the Middle East, and shut their economy down. Russian output cannot replace their needs.