Agreed. A game world doesn't need multiple ways of casting spells. In a lot of ways, it's best to pick one way and stick to it.
Back in the 3.X edition, we would have a discussion about this at every Session Zero. Before rolling up characters, I would ask the players, "Okay. How do you want magic to work in this game world?" and present them with a few options. If they voted for "book magic," there would be only Wizards in the game world. If they voted for "blood magic," there would only be Sorcerers. "Pact magic," only Warlocks. "Miracles from the gods," only Clerics. And so on. Once they had made their choice, all other spellcasting classes would be removed from the game.
The result is one unified spellcasting mechanic in the game world. In a "book magic" world, a cleric is a White Mage: a wizard who chooses their spells from the Cleric list. A Green Mage is a wizard who chooses their spells from the Druid list, and a Song Mage is a wizard who picks spells from the Bard list, etc.
Again, not everyone's cuppa tea. But I really liked it.