I don't disagree that thematically Warlocks have always been about taking whatever power they needed and forcing it to their will but Blizz wanted to go the other way and what I outlined is the archetype of a Master summoner which in a game like WoW is pretty much impossible.
A proper Demonology spec was what we had when Soul Link and demonic sacrifice were staples of that tree, forcing our enslaved demon to either shoulder the damage we were taking or outright sacrificing it so we could use it's power for ourselves (and ressing it so we could double dip, which is why my lock was an Eng.. good times). Clearly this does not fit at all with Blizz's class fantasy and it's an utter failure.
Warlocks are not nice, warlocks are pretty much bastards who happen to be on the 'right' side or that is what they had been up until Legion.