Again, you are looking through American eyes, similar to the Vietnam debacle. The only point of view that is relevant is the Russian perception and what they deem to be an existential threat. That is the key to military analysis: think from the adversary’s view point.
“I cannot forecast to you the action of Russia. It is a riddle, wrapped in a mystery, inside an enigma; but perhaps there is a key. That key is Russian national interest.” - Winston Churchill
I disagree that Putin sees Ukraine as an "existential threat" especially since NATO membership was not going to happen anytime soon. I believe Putin sees Ukraine as "Malo Russian", not even a country but an area that should be controlled by Moscow.
“It cannot be stressed enough that without Ukraine, Russia ceases to be an empire, but with Ukraine suborned and then subordinated, Russia automatically becomes an empire.”
― Zbigniew Brzezińsk
“The only point of view that is relevant is the Russian perception”
That is a very strange statement. Russia’s neighbors have their own relevant points of view. Russia doesnt get to rule the world just because the Russians feel like it.