I feel like, in general, 1-2-3 doesn't work with cast times. Note that no Job that exists with a 1-2-3 does so with the buttons having cast times and being subject to interruption.
RDM doesn't have a CAST 1-2-3. Its melee combo is a 1-2-3 but are Weaponskills. The closest to this would be PLD with Holy Spirit as a cast time Spell, but Holy Might...makes Holy Spirit instant cast. SMN's 1-2 are Spells technically, but are Instant cast. RDM's casting combo is variable, with a general "short-long" set of pairings, but even ignoring the proc chances on Fire/Stone, works using Dualcast, which makes the second cast instant. Dualcast is effectively a "Verthuner/aero Ready" proc that can just also be used on Raise and Vercure and (if you're weird) Jolt. Then on top of this it has Verfire/stone Ready procs to shift the rotation further, and the rotation also has no set rigidity; you balance based on your current White/Black Mana values, and even have the relatively short CD Acceleration charges to use to throw instants around.
Sure, in theory, it could be a 1-4-3-5-2-3-4-5--2-3-4-5 rotation if you always got Stone/Fire procs, but you don't, so the rotation is all over the place and not a rotation. It isn't a 1-2-3 to begin with, as it can be anything. It could be 1-4-2-5-1-5-1-4-3-5 as likely as it could be 1-4-1-5-1-4-1-5-1-4-1-5-3-4-2-5-1-4.
Also, PLD has the least rigid of the Tanks since its rotation is more a 1-2-3-4-5-5-5-1-2-3-4-5-5-5, but the -4- can be used anytime from just after a -3 to around and just after the next -2 with the -5s being shifted left or right based on where you want to use the -4. In this sense, 1-2 could be the same button/functionality, but the -3, -4, and -5 are distinct. There are times you might hit -4 or -5 between 2 and 3, or even 1 and 2 I suppose. Especially if you can use this to get two HS's within a FoF window.
Either way, I don't think a 1-2-3 combo on every Healer is the way to go. I DO think you could do something like have SGE with a 1-2-3 "ranged physical" rotation like MCH. That could be interesting...but that isn't what they went for with the Job.
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EDIT:
That doesn't really solve the problem. The people who dislike Holy would feel like they have to use Holy Stance when they need to move. The people that like Holy and dislike the Earth/Wind elements would be forced to use those that they don't like to do optimal damage.
The only way this would work is if stances were all identical except for the spell effects, where it was effectively a VFX toggle with no gameplay functionality, like Eos/Selene.
As long as you're trying to make it something related to gameplay, it isn't a solution since it still "forces" people to use the stuff they don't like, which doesn't address the concerns. That said, an Eos/Selene like toggle for spell VFX would be kind of cool. I don't ever see them doing it since it would be more work for them (even if they only add new animations for the Devs' current course and only use the existing Stone/Aero/Water ones from now on, and even if that was the deal upfront, within an expansion the Druid players would be demanding new animations for "their spells" too, accusing the Devs of treating them as "second-class citizens" even if that was the arrangement made to begin with...)