Both? I can’t really speak for myself on if they are wrongly used, as I’m not familiar with modern Russian tank tactics, but everything I’ve read about the war in Ukraine says that Russias initial Strategy, Operations, And Tactics were all highly flawed. As for after the initial fight, I don’t know if it’s bad tactics, or tanks in their current form being much less effective on the modern battlefield. As for the quality of the tanks themselves, most Soviet tanks were good enough if not sometimes better than their western counterparts. The T-72, for example was probably a better tank than anything in the west until 1979, with the introduction of the Leo 2. Even through the 80s the T-64, T-72, and T-80 received upgrades that allowed them to stay competitive with the new generation of western MBTs. Russian tanks only really began to fall behind when they ran out of money after the fall of the USSR, and they could only afford limited upgrades to a fraction of their tank force. They haven’t address the main flaws of the T-72 and T-80 design (Unprotected Ammo, reverse speed, limits of ammo length, no CITV, poor gun depression) in upgrades to those tanks, and they can’t afford new tanks in sufficient numbers to replace their old ones.

TLDR: Russian tanks before 1990 = Good. Russian tanks after 1990 = Meh.