Helped Ukraine much, did it?
(Controlling Denmark would help tremendously, too, which is why Moscow once asked Berlin for Denmark during or right before WWII as a response to Berlin's asking Moscow for its consent for Berlin to take control of Romania or some such.)
And yes, I believe that continuing to be able to access the world ocean from St Petersburg has helped Russia in its war with Ukraine.
BTW, "China ends up in either nominal or practical control of almost all of [Russia]" strikes me as so unlikely as to not be worth thinking about.
Who does, then? There doesn't seem to be any internal power in position to gracefully take power when Putin inevitably proves mortal; whatever the power scramble looks like, it's going to take external funding (and thus external obligations) to secure it, which leaves whoever's providing that funding in effective control. And even if the US and/or Europe decide to try to buy one horse, China clearly is willing and able to buy a whole lot of them; just statistically they probably end up with it, no?