Li Shenron
Legend
I feel like the sorcerer and warlock are only separate because of the warlock's separate mechanics.
Partly, but the main reason is more "social" i.e. the Warlock is a separate class because a lot of gamers liked it in 3.5e and 4e, and WotC wanted them to be happy in 5e too.
The narrative distinction between Warlock and Sorcerer is very clear: as a Warlock, you get your powers from a powerful fey/celestial/whatever, as a Sorcerer, you ARE the powerful fey/celestial/whatever.
If anything, there is a slightly less distinction between Cleric and Warlock: how powerful does the fey/celestial/whatever need to be in order to be called a deity?
But you can of course merge Warlock and Sorcerer, or Warlock and Cleric, or Wizard and Sorcerer or all spellcasters classes for what matters, if you like the narrative better in your fantasy setting, nothing wrong with that...