It's most perks on exotics that doesn't really work or it's so small and insignificant that the difference is hardly noticed. For a example the Gravitation Forfeit is supposed to increase invisibility but only does it by 1.5 to 2 seconds. they've removed the secondary perks from a lot of the returning exotics. with a few exceptions exotics or completely underwhelming and not worth using, at least until they fix them and not just buffing them but bringing the original secondary perks, like extra grenades.