I haven't kept up with some of the discussions but "The Chieftian" has had several videos on this subject.
His opinion is that lot depends on the upgrade/s. If you can fit modern vision equipment on an old tank you can get a useful vehicle, not first rate but useful.
If you have a more modern base tank but older generation vision equipment you are the target, it doesn't matter how good the gun/ammo and armor is. Your opponent has a better chance of seeing you first and you are trying to survive a first round hit and catch up.
Really old tank with good vision gets out of the way/hides and waits for the APCs to show up to brighten the night sky.