I actually agree with this. I still think you guys are worried about being a pink mage more than you like to admit, but I also think what you say is true. If RDM is "balanced" towards a healer slot, SE won't do anything else with the job. So I see your point and wonder what can be done to fix this.
I'm not afraid to admit it at all, as I did in =10 a few minutes ago. You want to be a ******* WHM? Level ******* WHM. End of discussion. Now, why would someone want to be a RDM in today's game? It's certainly not due to Abyssea procs, being a tier behind on nukes, a second-rate healer, or so far behind on the DD chain (without CDC) that people never even wanted the job for this purpose BEFORE the absurdity of Abyssea.
Now, my Regen musing is one step toward that fix. Slash's interpretation, though, isn't quite my angle. Instead, I'm looking at it more as a Dread Spikes we cast on others without it doing damage to the mob. Let's just call it Renew. Cast Renew on random person with 1500 max HP and for the next 10 minutes that get, per minimum, a 3000 HP regen pool that will tick away as he recovers damage. Higher enhancing magic will up both that pool and the maximum amount you can recover in a hit. So, if you're stuck at the 75% minimum rate, you'd need to take 4000 damage, and during that active time, at best recover 250 a tick, ideally 83-84 per second. And as I've pointed out before, stacking this with a 500ish HP Cure IV can give you a "reaction" to spike damage of at least 750 HP. Outside of Abyssea that's more than half the HP of a lot jobs and alongside the global cooldown delay, Cure IV's recast is actually manageable.
The real beauty of this, though, is if you do dump us in the DD parties (then again, DD tends to be tank now). AoE healing has NEVER been one of RDM's strengths. If you're stuck with some stupid party formation of you and 5 DDs (god, I do not miss these days of Dynamis), the duration of the spell and the pool basically makes this a preemptively cast Curaga II or III depending on how hard the AoE is. You can then pick the most immediate DD for attention while those at lesser risk will regen back to safer levels by the time you can actually get to them.
The balancing factor will be that the regen rate will depend on the last amount of damage received. If you took 1000 damage, then a second later 150, instead of getting that 250 the next tick, it'd be 37ish. From the RDM perspective, to minimize this inefficiency you WILL want your debuffs up to keep a mob slowed, paralyzed, and less likely to hit. You'll still get the occasional unfortunate situation where an -aga or TP move is followed immediately by a normal attack, but that also kills players under the eyes of a WHM. It'll still be useful for scrub mobs, too, and give us more time to do other things like nuke, debuff, or melee.
As was also noted, we don't overlap with WHM well. While I wouldn't expect this regen to "pause" at full HP, if SE went that extra mile, it'd definitely help our synergy with WHM and cut down on the overcures. Even without it, if in the same party, they'd also benefit from having it on the tanks. No, it's not Cure V. No, you wouldn't want to rely on it alone. However, I also feel people underestimate RDM's ability to heal things in Abyssea, in part due to actual party formations designed to make it fail.