I'm not going to say that NATO materiel has had zero effect but I think what Russians (at least those in power) really can't reckon with is that their initial invasion got stopped by Ukrainian AD, artillery, armor, and soldiers operating on the same Cold War stockpiles and doctrine as they did. The single most valuable intervention from NATO was simply alerting Ukraine that Russia was about to invade, allowing the Ukrainians to disperse their units.

Russia committed to too many (and often poorly chosen) lines of advance and did not have a plan to keep their units adequately supplied and moving on the approach to Kiev. This meant even in the opening month of the invasion, their plan went south almost immediately and you had infamous miles-long traffic jams on the roads leading south. Their SEAD didn't work. Their soldiers were not told ahead of time that they were invading Ukraine. They didn't want to mobilize ahead of time, so they didn't amass enough forces. Against a large country like Ukraine you don't need to invent a NATO bogeyman to understand why the initial offensive failed. Credit to Ukraine, they did not allow a defeatist narrative to take hold and fought.