DEI applies because the guy who builds the entire plane himself, because of it, cannot get a higher score than the guy who partially builds his plane. It would not apply if for instance, the score for building the entire plane yourself is 50 points and goes down from there. If you don't build your control horns, that's 45 points. If you don't build your wing that is 35 points, etc.
I think you should consider a class that mimics slot car racing where the track supplies the cars and controllers. A class where the AMA (or whoever) supplied the airplanes, control lines and handles, ALL BEING THE SAME, that would be a true measure of flying ability ONLY.
Giving someone points for an airplane they did not build their self tilts the pin ball machine, without the machine sounding an alarm and locking up.