I have a theory on those old tanks.
They have developed a tactic where they use a certain group as cannon fodder, then they attack from the second line and rely on numbers. This is a tactic from Wagner, but the main Russian army has adopted it as well.
They also looked into WWII tactics, when the Soviet Union had a million troops to invade Ukraine, so they want to use as many tanks as possible.
However, that won't work. For one thing, they don't have enough people trained to use those tanks well, plus they are too slow and the state they are in is probably not that good either.
It's true the German tanks in WWII were more advanced, and the Axis had a lot less tanks which were harder to service. Won't work though. Also German tanks were slower back then.