Some thoughts on core 5e classes.
1) [Wizard], [Druid], [Paladin], [Monk], [Artificer] are the strongest fictional identity among the core classes. No notes. They have an obvious identity and are easily recognizable as a class within pretty much all baseline D&D settings.
2) [Warlock] has a strong core identity, although its story is weakened somewhat since the patron can just as easily be an involuntary boon (or curse) as opposed to a proactive choice to seek power (the "normal" warlock story). When we're talking class as diegetic element, having multiple backstories lead to the same power progression isn't a virtue.
3) [Sorcerer] has a strong concept, but its story is all over the place; it also doesn't have a real narrative place in core D&D settings (other than "outsider not-a-wizard"). It mostly exists as a contrast to [Wizard].
4) [Bard] has a strong conceptual image, it also has a strong mechanical structure (in 5e), but the two don't actually mesh very well. The fact that different conceptions of [Bard]s can go from no-magic all the way to competitive with [Wizard]s makes inserting the [Bard] as a coherent diegetic element difficult.
5) [Cleric]s are one of my major pain points for diegetic classes. Why do people who follow gods who are completely in opposition still gain 80% of the same power set? [Cleric]s work with a setting with a strong medieval church analogue, but are really problematic to explain with a pantheon like FRs.
6) [Fighter]s and [Rogue]s are the worst. How do they stand out from the masses of "people who are kinda around", other than being, ya know, not dying quite as easily? I would take them out, or barring that, move their subclass to level 1 and attach strong narrative elements to the subclass.