As in almost every war, little goes to plan. Everyone miscalculated.
As I mentioned, war is 95% politics. It was politics that defined Russia's invasion. It would mass an overwhelming force at the border. If that didn't convince Ukraine (the U.S.) to negotiate it would roll in and scare everyone into settling.
IF Putin's regime really wanted a war with Ukraine it would have cut their communication lines, bombed military installations. That's what he probably regrets not doing.
Instead, it backfired and the Ukrainian used Russia unpreparedness to mount an effective counter-attack. Ukraine showed that Russia is weak (and it is). We think Russia is strong because of decades of US propaganda which serves to justify our $1 trillion spend on weapons, etc.
We're weak too (but another story)
Anyway, I agree with you. Russia can't pull out for many reasons. Germany miscalculated that it too, didn't have the power to tell the U.S. no.
So here we are, a proxy war between the U.S. and Russia. Russia has a lot of structural problems, which I already went into. It has no good moves. And Ukraine must lay in the bed it made, as you pointed out.
I don't believe the U.S. will come out of this as a win. Again, it comes down to politics. Now it's THE U.S. that looks weak. All its weapons and still Ukraine is where it is. And Israel, pissing everyone off. So again, I believe, much we agree on.