Daedric summoning is just bad mechanically. And you have entire sets built on the concept of 'pets' and they're the only ones that have it. I don't really understand that because I see plenty of sets that work for any class depending on their set up, but NO character can get pets, or would want pets based on how you've designed it (seriously, why didn't you just make it a 30 or so second summon with an active attached rather than a toggle? what a waste of time).
There isn't a lot of clases without a spammable ability either. Their dps, stamina or magicka, all comes from other weapon skill lines. They really need some love guys. New sets are great but they're just not fun to play. No one wants to always use the same 4 abilities. This game is really due for some more skill lines.