Camate,
I think a key point is being missed entirely. RDM and SCH were asking for Cure V to allow them to main heal parties on the newer content. If the development team is of the opinion that only WHM should be able to main heal, then a lot of time and effort is being wasted on these Cure adjustments.
Yes it is very silly that just about any job who can sub WHM can heal almost as well as a SCH or RDM. You can address that issue, but it will change nothing about either job's problem with a lack of a useful/needed role in a party. The possible changes you mentioned could possibly make the situation even worse (or not help at all.) The MND example isn't particularly helpful b/c unless you gear for it, the MND differences among jobs will not have a large effect. Cure potency gear will always be preferable anyway.
The other problem is by improving the amount healed by Cures III and IV and making these other changes to cure spells, you're actually helping WHM more than SCH or RDM. The reason this is a problem is because the reality of the game at the moment is that back-up healers are rarely ever necessary. I play WHM. I just about never need any assistance with curing. If whatever we are fighting is tough enough that I need help, I would need the assistance of another WHM and not a SCH or RDM. The only support a WHM needs is that of a BRD or COR, (or another WHM) who would ultimately add more utility to the party as a whole.
You've been paying a lot of attention to SCH lately, but aside from the 2-hour spells, not much has really changed. I was hopeful about the Regen changes, but if the position of the team is that you will not provide SCH enough tools (even without Cure V) to main heal a party, then these Light Arts boosts will change very little. Making SCH a little bit better at something that is ultimately not needed is really not helpful.
The issue for me is not the amount of HP cured or the strength of the Regen spells alone. It was about carving out a solid role for the job. (The comment about not giving one job's abilities to others cannot be taken seriously given what has happened to RDM and to a lesser extent SCH.) The areas where SCH and RDM shine are just not needed or effective enough to warrant bringing them.
If the development team is unwilling to bend on this, then it seriously needs to change gears. These Regen for SCH will change nothing. They need to instead focus on providing more useful support spells that are desirable to a party and that when coupled with the job's other abilities, makes for a viable choice to fill a support slot. Healing - DD - Support - those are your choices. You're crossing out the first and the second is not really an option. There have been so many great ideas about adding bonuses to weather spells, giving traits, adding new buffing spells, FIXING THE ANIMUS SPELLS, etc. but we've seen nothing about this.
Enfeebling magic needs to become not just useful but needed if RDM is going to find it's niche in the support role. Dia III is only going to carry the job so far . . . SCH needs better party buffs and the suggested TP debuff. This shouldn't be news to anyone.
The other (terrible) option of course is to increase difficultly on most content so that a WHM cannot main heal a party without the assistance of a back-up healer. Then again, even if that were to be done, do those two jobs bring enough to the table so that it wouldn't be a better idea to bring a 2nd WHM? Right now the answer is probably no.