Ben, good post. You have a firm grasp of the issues already covered in this thread. Your A-level choices are fairly broad and can be applied to other jobs other than pilot.
It is all very well focussing on pilot but many apply an dfew are chosen. A career in any other branch can be very rewarding so you, and all other wanabees, should keep an open mind for your choices.
University v Direct Entrant = there are no scores or comparators as such.
The view for direct entry is that we capture a suitable applicant before they are seduced at university and while their potential is still being developed.
The university graduate OTOH supposedly demonstrates a higher level of academic ability with better potential at higher ranks. This is offset by the habits and independence acquired at university and the declining apptitude as you will have peaked.
From your point of view as a DE you earn more more quickly and build up less debt but you have no degree on which to fall back. As a graduate you have had 3 years of enjoyment and life and a degree.