Unless you are in a situation where your plane is lower, slower, turns worse, climbs worse (F4F/109E) than your opponent (A6M5/SpitIX) then the pilot has the most to do with the outcome. Yes the plane is a big part, and flown stupidly (like I usually do) any "uber" plane can be kilt by any other plane.
Ultimately, the intangible in the equasion, the pilot, is what makes all the difference except in the most extreme plane matchups and even then the pilot is a huge factor.