In light of my answer, only way it can help is direct participation with their own units, not just supplying equipment. This is a line West is not ready to cross. Especially since it will only have considerable effect if Westnern planes with Western crews operate over internationally recognised Russian territory (over Ukraine-controlled territory Ukrainian air force dominates as it is, over occupied territory, there are few military significant assets). It means going from a proxy war to a real war.

> over occupied territory, there are few military significant assets

Are you sure about that? I'd say that the war could be ended rather quickly if Russians were attacked the moment they set foot on Ukrainian land. Also, an air force could destroy supply lines going deep into Ukraine.