Their lack of training is certainly proving their downfall. This is one thing the UK and other nations do well. Without sounding to big headed, I know for a fact the UK submarine and surface fleet are outnumbered but nobody can touch us if the numbers are even due to our level of training. FOST(flag officer sea training) is admired around the world and nato units come over to learn from them.I view it as a combination of over-estimating their own capabilities versus a poor evaluation of their opposition. They expected to waltz into Kyiv in days.
Once they've faced any semblance of opposition from a trained and resilient force, the standard of their military and its inept tactics have shone bright.
The sting in the tail is their nuclear arsenal, but as @john jako mentioned a while ago there's no actual doubts about how effective this would.
Clearly, any nuclear weapon could cause huge damage so it's not a case of totally dismissing them, but would a lot of them work - that's a fair question.
I’ve heard stories for years about the lack of training and training structure for the Russians. They have gone quality over quantity and it’s not really paying off.