There are no doubt that the United States is the largest arms exporter in the world and the majority of their revenue is derived from the sale of arms, which contributes to the growth of their economy. If there is no war, who do they sell weapons to, so I also agree with you that America is the mastermind of most of the wars in the world. No one benefits more than them, one way or another they are always manipulating all that chaos, unfortunately Ukraine has become the target this time.
This was is an exception because the benefit of US in this war is not monetary as we know they haven't been "selling" weapons to Ukraine but "donating" it with a huge billion dollar budget dedicated. Also this conflict is causing high inflation in United States which is damaging their economy. There is also a secondary damage as US dollar is being dumped as reserve currency slowly but surely.
The benefit is mostly geopolitical for US as every day Russia is stuck in Ukraine it is increasing the cost for Russia. Every asset they lose, their military becomes 1 asset weaker. This is why US is all for prolonging the conflict.
It also weakens Europe and increases their dependence on US while keeping the dumping petrodollar alive.
Considering USA has a bigger military budget than 25 next nations combined, Russia doesn't have a thing they can do about it. Sure USA wouldn't give "all" to Ukraine, there is no way, but they could keep on spending that kind of money and weapons and other stuff to help Ukraine until Russia is broke.
Definitely, it looks like Russia can do this much longer and they are doing financially fine "now", but the moment they realize they do not have too many more soldiers left to send, and too many weapons to attack with, I agree that those asset numbers will force them to stop and USA could prolong this as long as they want. They have the assets for it, and they are not the ones dying.