What people failed to see is "People" is not soldier. So more "people" in a country does not equate to more soldiers.......
You need to be seriously train to be a soldier and execute maneuver and tactics in war, if I just plug a person on the street and give him a rifle and tell him to assault, he/she won't last 5 second. And training/doctrine development take times, time Russia don't have.
The force regeneration aspect of war is you need to keep pumping up enough "people" in the pipeline and turn them into soldier, which require a large deal of resource, equipment and time. All of which is what Russia is lacking at the moment, any spare resource they have, any spare equipment they have, it would have ended up in the frontline first, and then they don't have enough time to train a soldier from nothing to everything. You need a year and a half to 2 years for that. That's why he is going after international PMC (a lot of African and Chinese merc fought for Russia in Ukraine) and the North Korean, the issue here is, can they sustain that effort with just that as well?