1. War sucks. There is a hidden cost to Ukraine the more years this drags on. This isn’t like the US where we have an all-volunteer force; it’s going to be more like the male populations of France and England post WWI. And the rebuilding process is going to be a whole other ball of wax that I’m sure will be contentious. I feel for the Ukrainian people and don’t want them to be at war for longer than is necessary.
2. You correctly point out that we’ve done damage to Russia far beyond our wildest dreams. At what point does Russia reach a threshhold where the regime feels threatened enough to resort to drastic measures, such as CBRN weapons (including nukes, but not only nukes) to signal their displeasure with how the war’s going. If we are to believe the “Putin is in poor health” rumors, that is another wild card which makes the regime unpredictable.
3. Parts of Ukraine (e.g. Crimea) are so pro Russian now that Ukraine may think it’s worth some territorial concessions to allow Russia to save face while exiting the war with (some) dignity. We all say that appeasement is bad because look at what happened to Neville Chamberlain. Well, also look at what happened to the Weimar Republic after it was humiliated and crushed by the victors of WWI, economically, militarily, and socially. Can we really forecast who will take over (eventually) after Putin, and what they will behave like? (Hint: One of the reasons Putin acts how he acts is because Putin felt his country was badly humiliated during the fall of the Berlin Wall and the economic chaos of the 1990s that Putin perceives was caused by meddling from West-aligned insititutions like the IMF, which is well documented in biographies on Putin such as The New Tsar by Myers.) My point is, a Ukraine war outcome that utterly humiliates Putin and his successor(s) - while leaving them with 2k nuclear weapons and a badly bruised economy/military/ego - is not on my list of good ideas.
For the above reasons, I’m of the opinion that the US and NATO should help Ukraine and Russia find an offramp within the next year or so that is tolerable to both sides. Prolonging the fight because we like seeing Russia obliterated and Putin humiliated may have unintended long term consequences that are bad for Europe.