Daedra were the focus of TES IV, so it made sense that they have a variety. Dragons are the focus of TES V, so daedra had to be put on the back seat.
But Oblivion had much more diversity in undead conjuration as well (2-3 skeleton, 2-3 zombie, 2 wraith, lich) , we got 6 different creature in skyrim, (3 atronach, 1 deadra, 1 familiar and 1 fire familiar), there were much more summon variety in both morrowind or oblivion. (golden saint, dwarven sphere, hunger and a few other were in morrowind as well).
More undead would have been nice.