>Putin did not expect it to be a fight at all.
I genuinely don't get this, though I agree with you. Still, how could Putin possibly expect Ukraine to roll over after the Maidan Revolution, which had clear and obvious western support? Perhaps he was nervous and figured that event was an actual threat to him? Especially given the United States', shall we say, cavalier attitude in selling arms abroad it seems really really obvious that Ukraine would of course happen to find themselves in possession of the latest in battlefield tech. Surely a lesson has been learned here, especially given that Russia's most advanced combat power has been significantly depleted in this endeavor - and without those modern weapons NATO can mop the floor with them using F-18s built in the 1990s. Same with tanks, not to mention drones.
Third,
>Because Latvia is a NATO member? American isolationists will say that NATO isn't worth getting nuked over anymore so than Ukraine.
Agree. I said this in another comment but I think it's pretty obvious that, 30+ years after the Cold War ended and the Soviet Union ceased to exist it's probably a good idea to assume there is some kind of priority list within the NATO members for who actually matters. I would venture to guess that certain former-Soviet countries that were added after the fall of Soviet Union are at the bottom.
Finally,
>Adding to the problem is the overly rosy picture of Ukraine successes in this war so far.
Also agree. When I discuss this with my too-well educated and too-well traveled friends, they sound like they've spent too much time on reddit. If you actually pay attention the war has somewhat stalemated, with slight favor to Russia at this point as they repair and rearm for what I assume will be a push to the western edge of the Donbas. Despite all this, these friends still believe in these now debunked myths (the Ghost of Kiev for one).
All of this just makes me want us to try to figure out a diplomatic solution. I don't know that Putin or Zalenskyy are in a position, politically, to seek one, so you may end up being correct that a compromise in one conflict leads, for Putin, to the initiation of another. I hope you're wrong.
Comparison to Germany in 1930s is fairly straightforward. Both Germany and Russia believed that they have suffered considerable humiliation in the last major conflict (cold war for Russia), lost "their" lands in the process, and were plunged into an economic black hole. In both, this triggered an embrace of irredentism and the overall ideology that can be summed up as "we'll be back, and then you'll be sorry". Both produced increasingly authoritarian regimes that, as they solidified their rule, started to look more and more at "their" lands among their neighbors. Both accused one of their neighbors of persecution of "their" ethnic minority, and justified the invasion and occupation of said neighbor on those grounds.
As for WW3 - no, I don't think it'll start over Kazakhstan. But if you wait long enough, it might start over, say, Latvia. The problem is that, with every country that the collective West allows Russia to overrun, NATO Article 5 is perceived as less of a real deal and more of a bluff. Basically, if US is unwilling to fight for Ukraine for the fear of escalating into nuclear, why would it fight for e.g. Latvia when the likelihood of that escalation would be even higher? Because Latvia is a NATO member? American isolationists will say that NATO isn't worth getting nuked over anymore so than Ukraine. So if you "draw the red line" there, you might find that line rather faded by the time Russia comes close to crossing it. They might cross it simply because they don't believe you have the guts to do anything about it by then.
Adding to the problem is the overly rosy picture of Ukraine successes in this war so far. Don't get me wrong - they are doing very well, exceeding all expectations by a large margin, and have plenty to show for it. But, at the end of the day, this is still a country of 50 million people with a $6 billion defense budget (2021) fighting against a country of 150 million with a $66 billion defense budget. Ukraine has had several mobilization waves since the beginning of the war, while Russia is still relying mostly on contractors and PMC. Ukrainian industry - which is largely in the east - is already devastated, while Russian manufacturing capacity is still fully intact, limited only by sanctions. If Russia were to truly switch to war footing to the same degree that Ukraine already did, Ukrainians won't be able to hold the line - not because they're bad at it, but because Russia can afford to overwhelm them with bodies and munitions. So you can't just assume that if we sit and wait long enough, the Russian advance will stall indefinitely, and that'll solve the problem long-term because all forces will remain tied in Ukraine.