Why Vincke believes that spell slots are are "unintuitive"?
Because in general people are dumb. More specifically, not every single copy of BG3 is going to be bought and played by someone who enjoys their sorcerer missing 37 times in a row and then permadying. The game is going to be purchased by people who have never played D&D before in any form in their life, and therefore, they'll need to be taught how that works. That is all there is to it.
It's the same with every game. Games need to explain their systems to players.
