It's a nice thought, but there's actually been a shift back towards Russia losing modernised/new production tanks in recent months in Ukraine. Although I suspect it may have something to do with Russia's ongoing offensives around Kupyansk and Avdiikva - a number of Guards and mechanised units got badly chewed up there.
Looking at visually confirmed Russian tank losses of known types since the start of October (165 identified by Warspotting):
T-55: 0%
T-62: 1.2%
T-64: 9.1% (of which T-64A/early B: 2.8%)
T-72: 54.5% (of which T-72A/early B: 24.2%)
T-80: 28.5%
T-90: 6.6%
For September through November tank losses were about 60% 'modern' (Russian made or refurbed) and 40% reactivated Soviet era equipment. That compares to a ratio of about 35:65 over June, July and August when Russia was in more of a defensive posture.
End of the day, there are still PLENTY of modern T-80s and T-90s and refurbed/updated T-72s and T-80s in Russian service in Ukraine. Estimates are that Russia has 1600 to 2300 tanks in theater, of which roughly 65-75% will be operational at any one time. You could probably say slightly better than half the fleet are 'modern' tanks.
www.thedrive.com
