> US when it was the uncontested superpower.

significant parts of the current world order evolved when the US was very much a contested superpower, c/o the USSR. While many things have changed since the dissolution of the USSR, many things have remained the same.

Further, you can guarantee that if Russia had announced in the days of war rumors re: Iran that they would militarily (not just intelligence & logistics, if stories are to be believed) support Iran, the US would likely not have attacked in anything like this way. That they did not doesn't mean that the US is "uncontested", merely that Russia wasn't interested in that sort of positioning of its own (nuclear) military threat over US action in Iran.