As you already know, it's because it's an exotic with the ability to intrinsically stun overloads. The reason tinashas's can stun all three is because it's a legendary. This all comes down to exotics having fixed rolls and legendarys having random rolls. Not every tinasha's has chill clip, and bungie isn't going to go in and make the artifact only work with those that don't have the perk. They can, however, do that with exotics since the perks aren't random. Is it dumb? Perhaps. But completely consistent with how much effort they typically put into these systems.