I think one way to possibly address this would (in addition to fixing the training pipeline) be to introduce some form of a 'below the zone' promotion fix to remove the requirement of being 'above average' in the air prior to being considered by the board-
Hmmm! I've no doubt in latter years the need to be 'above-average' for promotion was being awarded regardless of actual ability. I flew with plenty of newly promoted Sqn Ldrs that were competent but most certainly not 'above-average' !