Ok, BSO Dave, I'll have a go.
Firstly, it is generally better to get other people to fight your wars than to do so yourself. You save your own young men, and you spend less than actually engaging in the war yourself. The French ruefully referred to this policy as '
the cavalry of Saint George'. It is also a policy that the US has applied before, in particular during the First and Second World Wars.
The benefits, so far, to US interests have been enormous. The Baltic has become a NATO lake. The Swedes and Finns have applied to join NATO. Almost the entire world has expressed disapproval of the Russian attack and, hence, has fallen behind US leadership of the issue.
The Russian armed forces have been exposed as chronically incompetent and severely downgraded. As they are - were - a competitor to US interests, the Ukrainians have generously taken them off the board. Any idea, now, that the Russians can thwart US interests is absurd: can anyone honestly see them rolling through Central and Western Europe, which was the great Cold War fear? Similarly, the Chinese will have come to the dawning realisation that in Russia they have backed the wrong horse and that any attempt to take Taiwan by force, or engage in any more 'wolf warrior-ism', should be given some second thought.
Regarding the Black Sea, the Ukrainians have managed to sink the Russian's flagship; they and the Turks have prevented the grain blockade that Putin attempted to impose. The Black Sea is not yet a NATO lake, but the Russians are unable to impose dominance over it. Their fleet seems to be confined to harbour.
There is an additional benefit, so far as I can see, which is that - at no military cost to itself - the US can work out the benefits of its own equipment and tactics. It is obvious that air and sea drones are going to be of vital importance in any future conflict. I would be surprised if the Ukrainians haven't shipped back captured Russian equipment.
As I have written before, the US is paying the price for being the being the top dog. The benefits of that are a reserve currency, which gives the Americans lower interest rates and a generally stronger economy. It can arrange the pieces of the global jigsaw to its advantage. It is actually a small price for it to pay:
the white man's burden.
There is one final observation. I have no doubt that the Ukraine is an emerging democracy, with dubious public morality - the full story of Hunter Biden and his business shenanigans is likely to be pretty unsavoury. In this, it would be like Poland, when I first visited some 30 years ago (it had mafia gangs, corrupt police, and all the rest of it.) But there are obviously decent people there who did - and do - not deserve an unprovoked war against them, with obvious war crimes and breaches of the Geneva Conventions against a civilian population. Americans ought to be proud of the role that they are playing in this conflict.