Except in BECMI D&D, where 'mystic' meant 'monk'. Or the Dragonlance version of it that was some kind of cleric-spell-casting sorcerer. And druids might not be healers primarily. You can't win.
Seems like there were a lot of fun 4e classes like the warlord and swordmage that fell by the wayside.
Mystic meant psionics in a UA that didn't go anywhere. It means nothing now.
Only in a failed psionic UA did the Mystic mean Psionics. Usually in D&D, the Psion means Psionics.
The Starfinder Mystic (and its subtypes) covers the same thematic ground as psionics, druids, clerics, shamans, and more. It's basically the intuitive, deeper truths of the universe caster that is the counterpart to the intellectual, magic as a form of science caster represented by the Technomancer.
I doubt that they would drop the term "priest" either. But I did offer the term as something that could work for the discussion at hand.
Mandela effect, I guess. I could have sworn there was an old edition of D&D where the Psionicist was called the Mystic - beyond the UA.
I propose Leader, Striker, Defender, and Controller.
Those still sort of exist - the Bard gets healing spells here because they don't want to totally gut it's ability to function that way. But those roles were limited to the combat pillar, and 5e roles are trying to address the other two pillars of the game, too. Experts deal with the social and skillful and exploration pillars. Mages do too, but less from a skill check angle and more from a spell angle (Bards and Rangers enhance their innate skillfulness with spells; the three Mage classes mostly lack the skillfulness but get around it with smart spell use). Priests sometimes have skillful functions, but they're more focused on Defender and Leader combat roles than their out-of-combat social pillar and exploration pillar functions. They are indeed a hybrid sitting in the middle, much like the Cleric was back in 1e as the original half-caster that combined martial talent with magical ability.
Warriors are Defenders, Strikers, and presumably with the right specializations, Healers and even Controllers. That is to say, they're entirely focused on the Combat pillar. They MIGHT have some social or exploration or skillful challenges they are equipped to deal with, and some subclasses may dabble in magical abilities, but these classes are about combat, front and center.
4e characters dealt with the exploration pillar and the social pillar mostly via non-class features - Ritual Caster, Martial Talents, Skills Challenges, some rare Feats, and during Essentials, some class features that were seen as very out of place and considered by some to be ribbons given that they had no combat function. Utility Powers SOMETIMES were useful out of combat but they were almost entirely written to be combat focused because the game highlighted the combat vs everything else divide of D&D.
5e still has that divide, but various classes are better at combat versus better at other pillars. Heck, the whole reason the Ranger has been so broken in different directions over the edition was because they set out in D&D Next to make the Ranger the best at the Exploration Pillar - leading them to underperform in combat, while just not achieving fun in exploration since they either struggled or rendered the challenge moot to the point of the DMs skipping over travel entirely. This UA reels them back from TCOE in some major ways, though the changes to Hunter's Quarry are welcome; it does the same genie-back-in-the-bottle attempt with Bards, and to a much lesser extent with Rogues.
So while I appreciate the deep cut to 4e's roles, and find them of some use, this thema is almost like taking those, semi-combining it with the Power Sources that they formed a chassis with (Primal still sits in a weird place cutting across 3/4 of the class groups), and expanding them to the other pillars that 4e didn't lock to specific classes.