To be fair modern Russia is not exactly the USSR or Nazi Germany (let alone both of them put together). Their army was decimated (huge understatement) in Ukraine. Their demographic situation was pretty bad before the war. But now? If you combine the massive casualties (more than the US lost in Vietnam during over 15 years AND the Soviet war in Afghanistan (10 years)) with the exodus of working age males how can they ever recover?

It's an extremely cynical take but US + EU can pretty much afford to "wage" this war indefinitely as long they give just enough to Ukraine for it not to collapse and both sides continue throwing their men into the grinder. Russia is on a timer; it might take an extra few years and even if they don't run out of shells they'll run out of soldiers sooner or later (of course unfortunately the same applies to Ukraine..).