Putin can’t afford to lose, and just as the USSR in WWII, he can afford to lose a million or so personnel if that’s what it takes to overwhelm Ukraine.
Putin doesn’t have to worry about optics or popular support any more than Stalin did. The only way Ukraine will win is if Putin is replaced, and that will take either a natural death or a palace coup, like the one that is happening as Disney as we type—and unlike at Disney, Putin can whack all his opponents before they get a chance to overthrow him.
I believe you are mistaken.
Putin is not Stalin.
He doesn't have the secret police forces Stalin did.
He doesn't have the ideological commitment Stalin had from his troops.
He doesn't have the control over information Stalin had.
He doesn't have the population of young men Stalin had.