By every account Russia has the manpower to outlast Ukraine in this.

Wars don't end because you kill everyone on the other side. The American revolutionaries didn't murder every single English citizen on the face of the earth. Yet, they still won.

The point is to last long enough and inflict enough losses that the other side does not want to continue the war. In Clausewitzian terms, even if you can't win the Trial of Strength, you can still win the Battle of Wills.

I'm sure whoever is left in Ukraine once NATO is done teaching Russia this "lesson" will be so glad to have been a part of this.

Ukraine is an independent country that is completely capable of deciding for themselves whether, and at what cost, they want to keep fighting off a foreign invader occupying their territory. This is also part of the "Battle of Wills".

I'm not saying that NATO and its members don't have an interest in the conflict, but the tell-tale sign that you're regurgitating Russian propaganda is that in your arguments Ukraine has no agency.