Dw you made your point clear and it is making sense.
Where I agree with you is that there is not much room of effort on RDM to go beyond, because the basic core is really close to optimal rotation. So I see how that feels unrewarding because most of the gains are from team sync and not personnal improvment.
What people are worried about is that, if they were to change that, there is a chance that to avoid power creep, devs could add mechanics that end up also lowering the floor rather than just raise the ceiling, leaving RDM who don't want to spend hours on a dummy with poorer DPS (or a wider gap).
I really can understand that you'd like the ceiling changed a bit and mostly you want new ways to attein it (and personnal ways not just party synergy). But narrowing the gap is the goal they had on SB and you can clearly see the new classes were designed with that in mind.
What I'm looking for, and I'd like that for every class, is if the best of the best do 5600 DPS, the ones who make good efforts do 5000, then just playing the basic core (correctly, but just basic) would still give you 4400ish DPS. RDM has that, making progress and new fights really satisfying because you can enjoy them and not just be focused on your cockpit like BRD or SMN. Doing just the core on SMN for instance doesn't cut it. And you said you put SMN aside because of the "things to track" bloat. Or maybe I read wrong.
But if RDM complexification goes beyond your control, what are you gonna do ?
I can tell you from experience for SMN : they increased the ceiling, the skill gap is huge, and i really don't like being less effective with it than I was in HS. I tackle 2 or 3 dummies everyday, but since I've been playing for 2 years, I shouldn't have to do that. So I'm kinda pissed about it. And I don't really oppose to it for RDM, but I don't wish it on them, leaving many average Red mages sad for the sake of optimization of complexity or depth.
The way it is now I understand that having the same amount of effort required to go from 4400 to 5000 on RDM than say 3800 to 5300 on SMN, feels much more rewarding on SMN (or rather, unstatisfying on RDM). Now if they can make it so that doing the 4400 is simple, 5000 complex and 5600 hellish, but it would be the same for every class, it still would feel rewarding to be 5000+.