It depends on what perspective you look at it from. Solar is probably the most used warlock class for teams, though outside of Well, the class identity is lost. Arc, imo, needs a re-imagining from the ground up. It really didn't deliver identity for any of the classes, despite some being stronger than others. The underlying philosophy of arc representing speed and crowd-control doesn't feel like it does so in context of the character, its more like it is a separate element from character classes as a whole. All 3 classes basically do the same thing the same way (chain lighting via melee), with hunter just doing it better.