Weapons that don’t drop XP

I’m in an argument with a friend who is playing the game and all the DLC in order from the beginning. Which means he isn’t experiencing any of the DLC as intended since he unlocked the Darkana first, but I digress.

He was saying that he disliked Emergency Meeting and Unjust Vent, and claimed the enemies killed by them didn’t drop experience, citing that he was sometimes hundreds of levels behind after using them. This was news to me, but I’m not currently in a position to refute him and if it’s true none of the wikis seem to talk about it.

Is it true? If it is, what other weapons (besides the Pentagram at least) can inhibit levelling by not dropping experience?