Might be best to just give up on him and never expect that answer, let alone a good one. He's been rather antagonistic toward RDM's status back on Alla in the past, so it's unsurprising to see it here.

As is, it's hard not to see where RDM falls behind compared to others.
WHM: Cura(ga)s, Esuna, Native Status Cures, Solace, Misery, AoE Boost spells, Auspice
BLM: -agas, T5s, AMs, Enmity Douse, Mana Wall, Native Aspirs, Sleepgas
Melees: The only things a RDM shouldn't lose to here are a BLM or SCH, SMN depending on how you factor the Avatar.

The above only gets worse if you start throwing procs into the picture, as RDM needs a special sub to do sword and club stuff while not even having all the dagger procs for blue. Aside from light, we're mostly 2 per game day, but that's something BLM and SCH also have covered. So, there's nothing unique going on to convince people that having a RDM around is a difference maker or, on the curative front, a liability against more difficult NMs.

Upping the job's diversity isn't a bad thing. Some of us happen to feel it could be better achieved through melee and not limiting this to just damage, but also utility. You can stomp around until you're blue in the face thinking that's how it shouldn't be, but none of that addresses the increasing homogenization of the mage jobs subbing RDM, or in SCH's case, being more like a backline RDM from the start with better tools for both support and nuking.