“If Russia is turning to old Soviet technology, they have burned up their A list units.”
No they started with their old tanks and didn’t even bring their first modern tank into Ukraine until the beginning of May.
https://nypost.com/2022/05/05/russia-reportedly-loses-most-advanced-tank-in-ukraine/
There are only a few a very few T-90Ms. And they were not in sufficient numbers at the start of their invasion. A few weeks ago the main tank factory managed to finish 8-9 new T-90Ms and shipped them directly to the front lines. Without the embargoed Swedish high quality ball bearings tank production will come to a complete stop.