Voadam
Legend
I think it is a spectrum depending on the specifics and lore of the classes.Ah, this is a meaty post I meant to respond to.
I love reskinning, I do it all the time. But, don't the idea of "reskinning" and the idea of "classes as fictional element" exist in opposition to each other? I feel like the approach you're describing is actually a super common one, but I'm not sure if people always explore the inherent tension between the two approaches.
Wizards, as you described above, are the poster child for "class in fiction", because spells, spellbooks, and scrolls are both a primary source for their metagame progression AND explicitly fictional elements. More so than any other core class, wizards have to engage with the fiction to increase their powers.
Fighters and rogues are mostly class abilities narratively connected to mundane fighting styles, so it is easy to not call the classes out in the fiction, little reason to call out the classes as distinct things in the fiction, and decently easy to reskin. In 3e adding a fighter class onto a panther was easy for the mechanical bonus combat feats or rogue for sneak attack and not sweat the weapon and armor proficiencies they don't use. In 3e the difference between a warrior and fighter class is not really something that will be called out in the fiction.
Wizards, warlocks, and sorcerers are fairly specific lore that exists in the fiction. You can reskin to go outside the fiction though, so a warlock's eldritch blast can be reskinned to be a gunslinger type of concept fairly easily without narrative patrons and such depending on class ability choices and exist in a D&D world with explicit normal lore warlocks.
Mostly I don't feel a tension in most reskins next to the narrative normal stuff in the same world or alongside the different NPC/monster stuff. NPC wizard statblocks often have magical abilities that PC wizards cannot do and vice versa in 5e for example, which is fine for me. Magic is broad and I metagame what PCs can access of wizard stuff in the world.
For me the tension comes in on reskinning whether or not you modify the mechanics to fit the reskin narrative. A narratively non magical mechanist (say super tech) using the artificer class as the mechanical base has a couple of decision points on interactions with magic where it can make more narrative sense to modify some of the mechanics. Saying the normally magical artificer stuff is non magical can mean it does not pierce resistances to normal weapon damage but also that it cannot be dispelled or detected as magical effects or create tensions as you try to justify them being dispelled or detected.