Try to avoid a shooting war with Russia at all cost. Russia can tolerate casualties (we can't) as they showed in WW II. A shooting war with Russia is a brutal war of attrition.
Question: Why didn't the Americans take Berlin in WW II?
Answer: The cost would be 100,000 casualties. (It cost the Soviets 150,000 casualties.)
1: Russians ain't what they used to be, neither are Americans.
2: Poutine can't get away with what Stalin did and his hold on power although strong is far from absolute.
3: The idea of unlimited Russian manpower reserves is a myth.
3a: By 43, 44 they were running out of manpower and their retaking of lost lands was the only thing that saved them from being fubared
3b: They also benefited by having a lot of young bucks on American farms and factories providing goods at higher efficiencies allowing more Russians to be released for the front [Lend Lease]
4: Russia is now only a country of 145ish million, Losing the Stans and the Ukraine really took out their manpower depth. The Americans can draw on 350millionish, about 60 or so Brits, French, Italians, 80 million Germans, 40 million Poles, 20 Romanians, Spaniards, Hungarians maybe even 80 million Turks. At the same amount of bodybags it will impact Russian household far more than western ones.
5: Hitler. In WWII they were fighting an opponent hell bent on annihilation, the initial greeting of invaders with bread and salt quickly went away. No matter how much of a Putin fan boy a Russian is, none of them... NONE of them will equate NATO with Hitler.
6: It's been pointed out that Russians fight really hard for a cause that is right like protecting the motherland from Hitler or Napoleon, but when they cause is bullshit, like in WWI it becomes a lot more hit or miss. It has been said if Nappy made the war about ending serfdom the results would have been very different, and if Hitler was wiling to fake a nice persona again things would be different, even with Hitler they managed to get a lot of collaborator units and more so Hiwis.
en.wikipedia.org
7: It's all irrelevant anyway. If fecal matter hits the fan I doubt there is any interest to enter Russia proper. No need for it.
7a: If Poutine did invade Ukraine and got drivin out of both it as well as the Crimea and Donbass regions with all the bodybags and destroyed equipment plus the embarrassment I doubt NATO would never need to bother with regime change and Poutine knows it.
Also as to why the Allies didn't try to take Berlin
The plan was taken by the British
Chiefs of Staff Committee as
militarily unfeasible due to an anticipated 2.5 to 1 superiority in divisions of Soviet land forces in Europe and the Middle East by 1 July, where the conflict was projected to take place.
[8] Most of any offensive operation would have been undertaken by American and British forces, as well as
Polish forces and up to 10 divisions of the former
German Heer (Army), remobilised from POW status. Any quick success would be caused by surprise alone.
If a quick success could not be obtained before the onset of winter, the assessment was that the Allies would be committed to a protracted total war. In the report of 22 May 1945, an offensive operation was deemed "hazardous".
I don't know where you got that 100K dead figure from. It would be much much higher. You not only have to take Berlin but all of East Germany, and drive the Russians out of the rest of Eastern Europe and the Middle East and probably keep fighting them.
So in short your entire thesis is entirely wrong.