How would such a world differ if the only spellcasters were Warlocks and their variants?
No Clerics, Rangers, Wizards, Druids, Wagemages, Binders, Paladins, Sorcerers, Bards, Incarnates, Truenamers, Beguilers, etc etc...
Just Warlocks. Mind you not everyone is a Warlock, but the only people...