Lack training, lack of spare parts and logistics and lack of precision weaponry have severely hampered Russia's assault. The war has also made it obvious how far corruption has rotted the Russian military from within. How many billions did Putin spend that were embezzled all the way from the top down to the depot commander selling optics and spare parts from mothballed tanks to the Ukrainians?
It also shows what a difference motivation can make.
Armor without infantry and logistics has always been vulnerable to infantry. It's just even more so now.
This showed you how impressive Hitler was able to rearm a defeated Germany after World War I (1919 - 1939).
Now compare it to Putin "modernizing" the Russian military. (2000 - 2022) and this is the result we got.
Putin did have small successes. Crimea. Syria. Special Forces and planes are legitimate. But they are in small numbers. You can't mass produce that to what Putin needed in a conventional war in Ukraine.