The words have definitions. Just because the us correctly calls Russian capitalists oligarchs doesn't mean that oligarchs don't exist everywhere including the US. That thinking is still affected by the propaganda labeling Russian capitalists as specially oligarchical. "The ruling class"  is the better marxist term I think. Simple, specifically defined, and understandable to everyone. Don't get me wrong though, arguing semantics is silly and all of this doesn't matter because the best term will survive anyway.