Motivation would be a key factor. That's akin to the ancient story below*, but even poorly motivated troops that are well-trained and well-equipped can do better than the Russian Army is in Ukraine. Consider the US Army in Vietnam in the late 60s.
The Russian Army has failed miserably, including resorting to atrocities. This indicates poor leadership and morale low enough for many Russian soldiers to believe "nothing matters" since they won't be going home. Both of those stem from a lack of training and a lack of support from those who sent them to fight.
*An old man and a boy were walking through the woods when they see a fox chasing a rabbit. The boy says "I bet the fox will catch it!" The old man says "Probably not since the rabbit is running for its life and the fox is only running for its dinner". This can be tied to the Red Queen Hypothesis of evolution regarding "adapt or die".
https://www.dominicv.net/adapt-or-die/