DFC, yet again you're obsessed with numbers. NO student learning to fly is going to understand 'procedures based on 25 deg bank or rate 1, whichever requires the less bank' when first learning medium turns.
30 deg is used, because it's easy to use as the quick cross-check to validate that the visual attitude is correct - there's a mark on the artificial horizon. Same technique is later used for 45 deg steep turns. Same at 60 deg or greater; the only change in technique being that to arrest a descent must include relaxation of bank rather than increasing backpressure on the control column.
Teach people to fly aeroplanes - don't condemn them to the drudgery of airliner flying until they can fly light aeroplanes correctly and with confidence. Athough if they're doing the MPL course, they're probably like those veal calves that never see the light of day - and are stuck with playing 747s in Cherokee......
