Russia in 1939 under Stalin is not the same as 2022 under Putin. The big decision make is mobilisation. Finland had a population of 3.5 million compared to 40+ million in Ukraine. They won't be able to fight without at least partial mobilisation as seen by the types of troops they send (RosGvardia and OMON are police force not military).
It's demographics. Russia have a big demographic issue, worse than any other countries in Europe. If you only take into account ethnic Russians, it is even worse.
