He probably had quite alot of power, mainly due to his Anuic nature, as there isnt much known about the origins of Jyggalag he could be a Magna Ge, as he sphere is really more aligned with that of the Aedra.
Hmm, I like the idea of unlinking the planes of Oblivion and diverting magical energy from reaching to a particular plane of oblivion effectively starving out whatever Daedric prince is occupying it, you may even be able to starve them to death, make their particular plane of Oblivion vanish. It would need tremendous power and knowledge to do though.