Look, if you don’t support a class with specific skills for hybrid builds you aren’t ending in the black circle. A class should be designed as a hybrid so that the player effectively uses it as a hybrid. And if you design all classes as hybrids you end up with one big mess.
Allowing exists so you have bad/meme builds. This is different than a class designed to be a hybrid. The melee sorcerer from your example should not be able to achieve much with his sword when his class isn’t designed for that.