Assuming that Russian armored brigades will conduct and use their armor exactly as Soviet Cold War Era doctrine dictated could be hazardous to NATO's or other contender's morale. Nothing wrong with 40+ year old tanks as long as they can be put to effective use.
As usual it is a cheaper solution to upgrade 3 old tanks than to buy an untested new model if medium to large stock of old tanks are available.
I find these to be great examples of tank upgrade offers among many others of course:
https://www.army-technology.com/projects/sabra/
https://www.armyrecognition.com/weap...n_1903134.html