there are many people who call themselves marxist-leninists on this site who do not subscribe to anything marx or lenin had to say about inter-imperialist conflict.

This is a bad faith way to start your post on this and also doesn't make sense in this context. Russia isn't imperialist, so how is it inter-imperialist rivalry? Some reasoning on why Russia is not imperialist found here: https://en.prolewiki.org/wiki/Imperialism#Russian_%22imperialism%22

It is possible we're reading different posts, but in my time here, how I see Russia talked about is with the term "critical support" if support is given at all; meaning that (roughly speaking) the person supports them with regard to resisting the western empire, but does not support anything else about its leadership, necessarily. Russia and the US are far from equal powers dueling for hegemony, as a framing like "inter-imperialist conflict" might suggest, and it is not helpful to understanding imperialism or global conflict to reduce something to "both sides" simply because neither government is socialist.

IIRC, Mao goes into the concept in On Contradiction, of varying allying conditions with the Kuomintang and how that relationship evolved. I think it's a decent analog to what we're talking about here. Imperialism is the prevailing force of global power, not local reactionaries, and so some amount of allowance for that needs to be made in considering who is and isn't worth "supporting": https://www.marxists.org/reference/archive/mao/selected-works/volume-1/mswv1_17.htm

And modern day China seems to understand this and utilizes it to further an alternative to the western imperialist order. If they were only willing to have ties with those states who are controlled by a communist vanguard party, they'd have limited allies on the global stage, which would make it easier for the empire to isolate them, undermine them, etc.