This. Even if the warlock is my favorite class ever, I dont understand why ''how you get your powers'' have such a big impact on arcane spellcasters. I mean, we dont have different martial classes because I bought my sword instead of having it being gifted to me, or because I use it left-handed.
It has historic reasons. When they created the game, they wanted to make a generic spellcaster , that is the source of "magic-user", they wanted it to stand for all possible casters. The problem is, the creators of the game had a quite specific archetype in mind when they designed it. Thus the book, the emphasis on smarts, the hunt of magic as a reason to adventure. And those elements were core to the class. Yet designers treated this quite specific thing as if it was truly generic. And it showed.
Want to be a witch? spellbook, Want to play Circe the demigodess? spellbook, want to play Samantha or Jenny? spellbook, Gandalf? spellbook. A fairy? spellbook.
It was a square hole where we were expected to force pegs of all shapes into.
A few decades later the designers accidentally "found" the sorcerer when looking for an alternative to vancian casting. An I mean accidentally found, because the sorcerer was a vehicle for different mechanics. Yet, the different origin rang a bell, Jenny, Samantha, Circe, Sabrina, Fairies, Nymphs all of them fit better under that version of the sorcerer than under any other version of the wizard -ok, Sabrina fits under the 5e wizard-. Later another story with other mechanics was created and the warlock was born, fully cementing distinct origin/distinct class and mechanics.
If the magic user had been truly generic we wouldn't be having this discussion. But the wizard wouldn't be as iconic as it is. As long as the wizard remains as iconic and with that specific story, we will need alternatives for the other possible origins and approaches to magic. Or not, but that is the quickest way to tell a group of players you don't want them at the same table.
