Ah. So, here's the bit that gets me - D&D's magic system has many constraints that are plain and visible to the players that constrain what that "fundamental nature" can plausibly be - whatever it is, it must be consistent with the resulting game mechanics. And I've been playing this game for umpteen years, and have seen a bunch, most of which didn't really work very well.
And, then either learning that "fundamental nature" doesn't really change anything, because of that mechanical restriction, or I have to break the mechanics to give them something cool for figuring it out. I am not a proponent of leading the players on exploration that doesn't actually impact things..
I'd just rather do that in a system with fewer constraints, because then doing something interesting with it without being over or under powered is generally easier.
Ah, whereas I am very comfortable making new stuff which sometimes creates new rules exceptions in 5e.
But I’m also happy as a player to explore this stuff without ever gaining a non-standard mechanical benefit.
My Gnomish rogue/mage deals in circles, binding energy, invocation and evocation in the hermetic mysticism tradition, and is researching ley lines, energy transferral, and the ethereal plane (where he believes the ancient Fey went to, in a world where the Feywild is part of the world. I’ve made it very clear to the DM I don’t expect the truth of that situation to match the PC’s expectations, it’s just as fun to have the process lead to new theories)
What effect does that have on the mechanics? Well, it partly explains his custom feat that allows him to basically treat his wizard levels as making him a half-caster, rather than never progressing again unless he takes more wizard levels, but that is also a fix for lacking mechanical structures in the game, and the fact that moving him to the artificer class after the fact would make his abilities partly incongruent with the story thus far. I’m somewhat tempted by the forge adept from exploring Eberron though…
Anyway, point being, he can’t like, regain spell slots by using dispel magic through his “spell eater” blade, even though it would thematically make sense, because we aren’t home brewing that far to accommodate how magic works.
I get why you might prefer to play or run for such a PC in a campaign using a system that more directly accommodates his story elements, but I’d rather play him in the campaign with the story premises I built him for, that also suits everyone else at the table, and works “well enough” for all of our character types and the story elements and threads the DM plans on putting before us.