Hell, I'd let a PC have that ability if they wanted, assuming they jumped through the necessary diegetic hoops to get it. It's a 1-3 round partial incapacitate, it isn't like it's that dangerous.Go nuts. But, for me, why would I bother? No player will ever have that ability. It's largely useless for a PC any way since, unless you are attacking "classed" individuals, the ability has no effect. Which means that actually, it would be entirely useless against NPC's - NPC's in 5e don't have classes. NPC's in most editions don't have classes.
That's a purely meta-game ability that pretty much only functions against PC's. It wouldn't even function against a PC's pet or summoned creature. Well, other than dealing damage I suppose.
But it makes one heck of a cool ability for an NPC. Worked absolutely fantastically when I used them in my last adventure. Total shock on the faces of the players when you tell them that their main caster just lost all their spell casting ability.