I have to slightly disagree that Russia has the best military, it's just the fact that they have the advantage in Ukraine at the present moment.
If they were to attack a NATO country (like Poland or the Baltics) it would probably be not so advantageous for the Russians, especially if other NATO members get involved simultaneously.
I'm not talking about Russia military versus Ukraine military. From what I read, some of the reddit volunteers had actual experience in the US military. But- fighting Russia is fundamentally different than when the US fought the Taliban. I don't think the US military is ready to fight on a level playing field against the Russians. They are used to things like fighting poor goat farmers in Third World countries. In no way am I denigrating the Afghans by saying that, their winning with limited resources only makes their victory more glorious, but there is a big difference in fighting the Russians.