1. Crimea is a settled issue. You may not like it and the referendum was obviously flawed by repeated Western polls since 2014 have shown annexation by Russia to be widely popular (~70% support). So much of this post talks about agency. What about Crimean agency?
2. While Russia is the bad guy here without doubt, you can't gloss over Ukraine's failings here. Stop with the binary thinking here that one or the other is wrong or that criticizing Ukrainian actions is victim-blaming. Prime example: cutting off the water to Crimea following 2014 by any objective standard is a human rights violation;
3. Ukraine has been a pawn for US foreign policy. It's wild to pretend otherwise. For the US military-industrial complex the current situation is basically ideal. Russia is mired in a war they cannot win, Russia has been isolated from the international community, Europe is set to become less dependent on Russian energy exports, NATO is strengthened and the US gets to sell lots of weapons to Ukraine.
4. The idea that Russia doesn't want a buffer to NATO is laughable and hypocritical. It ignores 200 years of the Monroe Doctrine where the US will not accept any foreign military presence in the Western hemisphere (it's self-declared sphere of influence). This was practically tested when the US almost started World War Three over a Soviet presence in Cuba. So why is that OK for the US but not Russia?
5. These authors make the same mistakes most US wonks do: they view the US as benign. Even if you agree with that you should at least accept that not everyone else does and there's plenty of evidence it isn't. I mean NATO's raison d'etre was to destroy the USSR. The USSR is gone so now it's by default the destroy Russia alliance.
6. As for the diplomatic solution, there ultimately will be one. There always is. Even unconditional surrender is a diplomatic end. Russia is a nuclear power. The pre-WW2 standards of defeating hegemonic powers just don't apply any more. There's a whole straw man bit in this about how the only alternative is unconditional surrender. Nobody is saying that.
I think the only thing I agree with is the justification for the invasion (most notably "denazification") is completely ridiculous. This is propaganda and it's what imperial powers do. It's really no different to the US spreading democracy in Iraq and Afghanistan.