Has Russia been holding back any of it’s best troops, tanks, planes, missiles, bombs, etc except it’s nukes since the war began?
Only Russia knows that. I'm only suggesting that it doesn't make any sense that a country as big as Russia, would throw all their eggs in one basket, use all their big guns up front, instead of sitting back, and just letting the U.S. and Ukraine eventually do themselves in, especially if the actual goal is to weaken the other side's ability to conduct war. Let the other guy blow his load.