Well, given that most ST fights are bosses and you won't be able to proc sephuz anyway (unless they cast), I'd say that Infernal was suggested as pet for trash. You're correct on the 1 min, though, which - to be very honest - is an absolute joke, given that it is one of THE weakest aoe stuns in game that has the longest CD.
Thanks for the tips. Howl is unfortunately not available to me because I'm Ally. So coil it is. Just a different thought was the knock-back from the succubus, but then again, the succy itself will probably be a bigger damage loss than the gain from Sephuz (if it works at all).