Since the jump to 6.0 is definitely going to cull skills to make room for new ones, let's start there. Beyond a certain point (literally the point when you unlock the tier 2 equivalents in my opinion), the tier 1 "Cure" spells become obsolete. Make Cure upgrade to Cure II, Benefic to Benefic II, and Physick to Adloquium.
Leaving tier 1 "Cure" spells on the bars act as both wasteful bloat (like Blizzard II and Fire II for Black Mage, oof) and promote unhealthy playstyles (cure spam is bad). Not only that, but there are traits in WHM and AST that try to convince players that Cure and Benefic should continue be used!! Go away, Freecure and Enhanced Benefic!
Sure, by removing tier 1 healing spells when tier 2 appears, it could make the 30s of healing a bit harder, but actually it's a good learning experience?
White Mage
They get Cure II at 30 and don't get Regen until 35, so Cure II would be their only single-target heal for those 5 levels. However, healing potency is monstrously more powerful at those low levels. Cure II is expensive, but all healers get Lucid Dreaming at Lv24, so it's the perfect time for healers to learn proper mana management. Cure II spam will drain a healer's mana, so they'll (hopefully) realize they don't need to overheal quite so much.
Astrologian
They get Benefic II at Lv26. Really, AST is the job with the least worries in this change because they already have Essential Dignity at Lv15. Not only that, but the mana economy of Benefic 1 and 2 are exactly the same (Bene1 is 400 MP for 400 pot, and Bene2 is 700 MP for 700 pot). They also get Draw at Lv30 which is 800 free MP every 30s.
Scholar
Scholar is the odd one out. Their Adloquium is at Lv30, but it's not exactly a "Cure II" equivalent because of the shield. Things could just be left as-is because fairy healing is bonkers at those levels and have SCH learn how not to waste shields by needlessly overwriting them via spam, or...
The other option would be to swap when Lustrate/Aetherflow and Adloquium are learned. Move Adlo up to Lv45 and Lustrate/Aetherflow down to Lv30. SCH keeps Physick until Lv45 while also getting early access to their primary healing aspect: off-globals. They can start learning how to heal with off-globals as soon as they unlock the job instead of waiting 15 levels.
TL;DR Please delete bad healing spells.