It's not the same Russia now, and yes I do know history, and I was overseas 3 years in USAFE, in a work center that studied the Russians. The Russians have land and no people to replace the loss, and a very low birth rate.
The other factor is the rank and file Russian Conscript wants no part of fighting Ukraine.
This all with a loss of 500,000 Russian Troops up to now.
Of course it's not the same Russia now. They are no longer a commie nation, or do you have sources on that too?
If any person in any country these days wants no part of any war anywhere in this world today, they should be patted on the back, instead of choosing to be cannon fodder in another proxy war.