I don't think there's any evidence Russia is suffering especially high losses (compared to the past, but also compared with Ukraine right now, which is arguably what matters most to the outcome). It also doesn't make any sense to me.

Russia seems to have superior firepower in all areas, except recently, the pro-Ukrainian side has been talking up the Ukrainian "drone wall" that's supposedly preventing the Russians from advancing, as well as supposedly improved tactics and deeper drone penetration. Just last year they were marveling at, and complaining about, the supposedly superior Russian Rubicon drone units.

I find it hard to believe that they turned the (self-admitted) disadvantage in FPV drone operations around in a year. I find it hard to believe that something about the Russian infantry tactics would explain high casualties, as both sides use similar tactics. I do not see why Russia's slow advances would expose them to especially more drone fire than Ukrainian defenders, given that the drones can operate tens of kilometers behind the front line. I do not believe any propaganda about supposed mass meat assaults or whatever they're spinning.

In all other weapons systems (except Starlink I guess), Russia seems to have an undisputed advantage. There is also literally no reason to expect Ukrainian soldiers to be better motivated, trained, or lead, quite the opposite.