(I will stick to the ethical and political philosophy analysis, and otherwise ignore the noise, in order to limit my participation to what I have the time for.)
America, Germany, Ukraine, Russia--and every nation in the world--are fundamentally irrational and immoral, living in an anarchy that is misleadingly called the international order. Yet, this does not change the fact that each nation has a moral obligation to defend its denizens from aggression.
Ukraine's position is unequivocal: It was and remains invaded by Russia, and Russia's excuses--whether or not Putin actually believes them--do not change the fact that Russia is the aggressor. Nor does the fact that the Ukraine government is far from ideal make Russia less an aggressor. Ukraine's has an obligation to do pretty much whatever it must in order to defend itself from Russia.
Russia is not an immediate danger to, e.g., Germany, never mind the United States. But its stated intention is to subvert the West, to bring it under autocracy or worse, and it has used violence and clearly intends to continue using violence against its neighbors and--without geographic limitation--individuals in order to effect that end. These make Russia a present-day aggressor, against which all threatened nations have an obligation to defend their denizens from.
That, of course, does not entail making war on Russia. Just as there are many ways to aggress, there are many ways to defend. I won't be going into that further, as that would take me far afield from the ethical questions. The key point is that the obligation of a government to defend its citizens does not cease to exist because that government is corrupt or otherwise immoral.
There is one other important difference between the positions of Ukraine as opposed to that of other nations. Ukraine is not and cannot be a liberal democracy, never mind an ideal state, while it is presently invaded by an aggressor power. To condemn it merely for failing to act as a liberal democracy is to condemn it for failing to be a contradiction. This is not to say that its political behavior is beyond condemnation; rather, it is a requirement that any condemnation take into account that it cannot be a liberal democracy. There obviously must be some limits, else it becomes a worse evil than its invader, but "That's not democratic" is not one of those limits.
This simply does not apply to other countries; they aren't threatened by invasion (yet). Their obligation is to move themselves closer to the ideal--toward limited government and individual rights--and there is nothing in their situation that negates that obligation. So, even though Russia is an existential threats to other nations--if not currently to their territorial integrity, to the lives of its denizens--those nations remain subject to the requirements of a nation not under attack.
It isn't proper for such a country to make corrupt military decisions. Not because they're military, but because they're corrupt. And by the same token, it is not proper to condemn a corrupt decision as a wrong military decision merely because it is a corrupt decision; the two characteristics must be judged separately.
As it happens, you are simply wrong when it comes to Russia's threat to the US. Certainly, it is not an immediate and serious threat, but any analysis needs to take into account the long term. A Russia hobbled in its economy, devastated by a defeat in Ukraine, and beholden to another would-be world power (China) that regards Russia as a competitor would not be a meaningful threat for the foreseeable future. A Russia emboldened by success in Ukraine, with an economy geared toward war, surrounded by nations cowed by Russia's military and economic power, on which Russia might draw for aid, and aided (and maybe even goaded) by China is an actual threat, one that could go full-on nuclear. (No, there is no reasonable possibility that the present war will go full-on nuclear, so long as no one attempts to invade Russia and maybe not even then.)
The purpose of any action in relation to the Ukraine war must be to prevent the latter scenario. And the most obvious way is to provide material aid to Ukraine and let them do the fighting. (Well actually, the most obvious way is to assassinate Putin. But the fools that run our governments don't like assassination as a tool, since they fear that it could turn on them. And even if they would go for it, it would be very difficult. Still, I could wish that the effort was being made.)
As for your observations about Ukraine's history, I hope it is clear from my analysis that they don't really matter. Sure, Ukraine hasn't exactly been a bastion of law and order, but that's simply irrelevant to the present war or to the US's interest in Russia losing this war.