I've always said this but When job design is good it enhances the casual content and even savage encounters.
Currently playing through content once is really the only unique experience you will get with that form of content, take savage raids for example once you do it on one job theirs no real point doing it on another, especially if they are in the same category of tank/dps/healer.
picking a different job should feel interesting and unique, maybe even challenging, but instead it feels pretty much the same because job design is so one note.
Healers like you've pointed out are a great example of this, but in general they cannot design anything other then a DPS role in this game (even this is becoming questionable), they have to give tanks absurd defensive kits that get stronger each expansion, they have to bloat healers with extra heals that doesn't get used because encounters still design around healers who only use gcd heals lol, this also results in no evolution in DPS kits, I guess people complaining made them add one skill dps you use to in 2minute windows.. enjoy?
Support roles (tanks/healers) need a massive overhaul with how they interact with the game, but my bet is 8.0 will mostly only focus on dps, because I have a feeling that they have no idea what they are even doing at this point with tanks or healers.