It's not necessary to utilize a MP gauge if it's not thematically appropriate for the job. Some jobs just don't manipulate aether. This is not a new development in the series. In FFIV, as an example, your party's Dragoon, Monk, Bard, and Engineer permanently have 0 MP.
What would be more useful is if there was a setting to toggle off your MP gauge on jobs that don't use it, and a setting to have the simplified job gauge elements automatically snap into position next to your HP/MP bars. I also think that the Skill Speed/Spell Speed system should be merged into a singular Haste stat such that the design is more fair for gish jobs. It's nice thematically to have a few Spells instead of Weaponskills and vice versa, but your stats should benefit all of your GCDs. If that's not feasible due to technical issues, they should just change both stats to have the same effect.