Ok, I think you misunderstood me.
Demon form was something given to Illidan and demonhunters in warcraft 3. it was their tier 4 ability, the most powerful and significant one. they also had an immolation aura. Basically, they were those guys that imbued themselves with demon powers to fight demons. And that class (and Illidan himself, in both his winged (spac) and non winged variants was probably one of the most liked characters in the game. So much edge, so many cool looking glaives. You get what I say.
Then came WOW, and demonhunters not being included as a playable class. And, in that regard, not using a cool ability like metamorphosis was a waste, and it made sense for warlocks, as they had things in common with both demons and demonhunters. So Blizzard gave them that… in the laziest of ways. They literally copied the W3 demonhunter’s demonform.
Obviously, warcraft being what it is ( a highly derivative fantasy world that proudly says “this is my lore. If you don’t like it I have others”) created their own explanation for this, but let’s face it: once demonhunters went into the game, giving them demonform made sense BECAUSE IT WAS THE ONLY REAL THEME THE CLASS HAD, and it was a class people wanted in the game for years. For the different classes to attract players, they need to be unique and different. And obviously that is not going to work when the main ability of two classes (or a class and a specc) is the same one.
Demonology warlocks, on the other hand, can be themed in a lot of other ways. You can make them summon powerful demons. You can make them summon hordes of weak demons. You can make them transform into demons, which don not necessarily have to be Illidan/Balrog looking. Any of those themes, or a combination of several of those, coulde work. Thus, taking metamorphosis from locks made sense.
Personally, I disliked demonform when it was added because it was an obvious, lazy rip off from the demonhunter’s demonform. So getting angry because they got it back makes no sense to me… it was never a warlock thing, no matter how much blizzard invented lore to justify it. Demon transformations for warlocks could have stayed, but It would have required it being reworked into something significantly different.
That does not mean that the current demonology iteration is something I enjoy. It is stupid, artificially complicated, and full of bugs.
personally, i would have liked demonology to be more about summoning powerful demons, sacrificing them for situational buffs, etc. it actually being about controlling the the pets to actually see them doing the fighting instead of just them being nukes with elaborated animations that can’t properly change targets.