its just my opinion. from korea&vietnam americans came to dominate the skies over russia built planes.
plus (at the time) the USAF and the luftwaffe would run mock training maneuvers and combat situations with the f15vs the mig29 every september (they have an official name for it, cant remember).
from there training they came to the conclusion the f15 was a much more superior plane over the mig29. beating it 15 our of the 18 engagements they played.
In korea & vietnam you did not have russian pilots (well you had less than ~5), so what good is a good airplane if you don't have a pilot that can fly well? USAF training was/is not comparable to korean of vietnamese. Also as far as I remember US pilots had a lot of trouble with Mig-15s in korea, and most of thous were korean pilots, vietnam did not seem so easy either.
Take a look at what USAF really thinks about the Mig-21:
http://www.youtube.com/watch?v=reVZ9aPYi9A&feature=relatedWould you have an official report for the F-15 vs Mig-29?
I'm not saying that Russian airplanes are better, but I'm not saying that US planes are better either. (at least of that time)