great point. i did the test because every kart setup document ive ever seen, to illustrate the need to lift the inside rear wheel, asks the reader to turn their wheel full lock and try to steer the kart. it also asks the reader to notice how difficult this is to do BECAUSE BOTH REAR WHEELS ARE ON THE GROUND
now im wondering if the freeness of a kart derives more from the front of the kart than from the rear. i mean- even if both rear wheels are on the ground, they are pointing the same direction. if the front wheels are pointing in two different directions wouldnt this cause a bigger binding effect than the rear wheels?
but i agree with your point. at full lock the wheels are going different ways and it wont move. what i find very interesting is that on the track even though full lock is not in play, it still rolls free-er with less ackerman and caster.