The intention of the Schism change was actually to make sure you _could_ use it every other Penance. Because it has a cast time, it's cooldown is effectively slightly longer, so it always didn't sync up at 18 seconds.
Nothing is inherently wrong with taking every available non-Atonement-improving talent and varying the playstyle away from the default, modulo correct tuning on the talents. Shadow Covenant is a new mechanic that thus far hadn't gotten much attention in testing, and if the most recent buff turns out to be too strong, that will greatly help narrow down the correct tuning.
Hey Shadow Priests. Let's talk a bit about utility.
Shadow in Legion currently has a ridiculous amount of utility, way more than any other spec. I talked about that in the previous thread, here:
Shadow is in a very odd situation when it comes to utility, especially in PvP. The amount of potential utility they offer is astronomical. It’s a staggeringly long list: Body and Soul, Dispel Magic, Dominate Mind, Mass Dispel, Mind Bomb, Power Word: Shield, Psychic Horror, Psychic Scream, Purify Disease, Shackle Undead, Shadow Mend, Silence, Vampiric Embrace… probably something else I’ve forgotten offhand. But at the same time, despite the crazy number of utility spells at their fingertips, it’s actually quite hard for them to actually use many of them. Since their rotation is based on continuously generating Insanity as fast as possible, any time lost to utility is punishing, especially in Voidform, where you’re actually losing Insanity while casting other things. And then on top of that, many of the spells cost huge chunks of Insanity as well. We’re not happy with that situation, and are considering other potential options. They could probably stand to lose at least a couple spells off that list, but we’re also considering bringing back Mana as an additional resource that would just be used for limiting your usage of the many utility spells, with costs proportional to their impact.