I think the problem with this is it's one of those designs that's fantastic on paper but doesn't work in the real world. ANYTHING related to damage will never be "optional" in a realistic sense. Utility, sure. A RDM that can throw in Verraises seemlessly in its rotation is great. A RDM that only uses Jolt (not Fire/Stone) is not, because in real terms the latter is hampering the party while the former MAY (situation depending) be providing redundancy (generally speaking, Healers get the first two KO's per minute, RDM/SMN should get the third or get the raise if it's one of the Healers that went down, or more than 2 people went down)
We see this a lot where people propose ideas of low skill floors and high skill ceilings, but because the skill ceiling adds significant damage, people who aren't reaching somewhat close to it are unable to clear content, or are considered to be harming other players due to their lower personal skill.
The problem with "Optional to master" is when it's never optional. No one requires perfect 100% gameplay, but players are still not allowed the "option" of significantly lower damage in content that is based around Enrage mechanics.
This is also the problem with the Job idea. For example, if we make all four healers play like SB SCH, many people would quit the role since they'd have no viable choice anymore. Whereas leaving one or two closer to what they are today fixes that problem, where players so inclined may pick which of the two they like better. This is especially true when it actively plays into the Job fantasy. For example, while one could argue for GNB or PLD to be skillful, technical combatants, WAR being unga bunga actually fills the Job fantasy of playing a raging berserker.
I do agree with you on the "less can be more" thing with buttons. A number of Jobs have extra buttons that largely just...exist to exist. Like Goring Blade on PLD right now, or Sonic Break in GNB. They don't add anything to the rotation, have no resource basis, and don't interact with any other mechanics other than they're used on CD in a buff window (but what isn't?), leading them to just be clutter that doesn't achieve anything useful.