Nah, demonology was not fine. It was a confusing, clunky mess, though it would've been mostly fixed by just turning Metamorphosis to a cooldown instead of a stance. But they just made an even bigger mess instead.
Yeah, I wasn't in love with WoD's version of Demo and was really looking forward to the new pet-focused version in Legion. I assumed they would actually make a fun, effective spec, because the idea behind it was very cool. Needless to say I am disappointed.
It really is a shame that Blizzard is so averse (or unable?) to enact significant mechanic adjustments to classes and specs in anything other than the X.0 expansion pre-patches. Demo needs some serious work if it's going to be a worthwhile spec at any point in Legion, and its core mechanic (demonic empowerment) basically needs a total rework.
Like, I can't say this enough: Demonic Empowerment is
bad. It is straight up bad game design. It's a failed design choice and they need to accept this so that they can start fixing the spec.