Easy fix is to just rework cure formulas so healing skill has a bigger effect on potency
It would have to be pretty severe for a smaller amount of difference.

RDM/SCH or anyone /sch alone starts off at a base B(-?) capped White Magic skill, then you can add cure skill gear that SCH and RDM both have decent amounts in, not to mention the cure potency amount accessible to them.

The problem doesn't lie necessarily in that sort of regulation, as much as it is the vast imbalance between DD/Melee jobs and cure/support jobs. Meaning those support jobs get shoved into the smallest number of slots possible no matter what. If you make RDM or scholar a competent healer on top of whatever else they offer, then WHM ceases to become worthwhile, because curing is the BULK of what they offer, where as RDM and Scholar have their respective nukes buffs and debuffs to fall back on or assist additionally on top of being the designated cure bi-... bot.

If they're not, and the focus is instead placed on making sure their unique contributions are viable enough to possibly bump a DD off the roster depending on what's available, then their healing could be brought up to a decent enough level where it does not outshine what they're supposed to offer as a whole, yet can support or take over LIGHT loads.

However, as it stands now, SCH and RDM can still handle light curing loads, so there's no need for Cure V. And if their contributions help mitigate overall damage, it'll likely stay that way. And in questionable situations, it allows for jobs like Dancers and Blue Mages to shine in their support aspects.

So really there's not much of a strong argument for giving out the spell, except for the desire to bump WHM off the throne as the go-to healer.