Um - in a lot of the big "next gen" or graphically acclaimed games of the time - FC2, STALKER, FEAR, WiC, Call of Juarez, etc. the GTX480 was a clear 30% faster than the 5870 at the kind of resolutions and settings people were actually gaming at. In older games sure it was more mixed with some trading of blows and Crysis partly due to being CPU bound was more even results. At the end of the day it was rarely slower than the competition and outside of a couple of extremes when it was slower it was insignificantly so and quite often significantly faster - that is generally regarded as retaking the performance crown. Take a look at the DX11 results there and elsewhere and more often than not it isn't even a competition with the 5870 a long way behind unfortunately that review only really covers Metro 2033 which has some dubious optimisation issues
https://www.techpowerup.com/reviews/NVIDIA/GeForce_GTX_480_Fermi/27.html
Regardless that is a very different story to Vega where comparing like for like against Pascal you rarely find results that offset the complaints about heat and power you talk of.
Most people in 2008-2009 or so were still playing at like 1680x1050 resolutions and a lot even less than that - 2560x1600 was used by relatively few - where the 480 even in that summary of performance has a 15% overall lead.