It's not a matter of raw population, it's a matter of how many losses a country is willing to take, and the defender will always have the advantage in that situation. Yes, yes, oligarchs don't give a shit about casualties, but the Russians themselves tore down two governments in the space of a century over the combination of a bad war and a bad economy. If Putin has to step this up to the point of not being able to pretend the draftees are there by mistake, or worse yet, hold an emergency draft, he's going to be walking on some dangerously thin ice.