Mr Wockip

I'm curious why you'd want to disable an optional thing in the game

It could be that because any companion can choose arcana they would need to have vocalizations for casting, assuming you make them when using scrolls (I don't recall)

I think something like this could be an easy to implement toggle option on game settings. Personally would prefer it if my companions stayed the same level as the player character for the same reasons as the OP.