The Ukrainians are defending themselves. Russia is the aggressor, I fully agree, I'm not saying otherwise.
However, I wouldn't be surprised that the west/NATO has gotten involved to such an extent because they want to see what fighting Russia would be like/to test our weaponry against their defences.
We had no obligation to step in and defend Ukraine and hit Russia like we did so I think there's more to it. Thus treating it as if it's a proxy war. We're using someone else's troops but they've been trained by us and are using our weapons so surely that's at least the definition of doing something by proxy, even if it isn't the literal textbook definition of a proxy war.
Its great power competition. The US and NATO are far more powerful than Russia and are penalizing it for stepping out of line. Caring about the welfare of Ukrainians by not wanting them to get carpet bombed into oblivion is also factor. Both of these can be true without being in conflict with one another.