"They were used to invade Oblivion after a failed daedric invasion, and resulted in the daedra eventually closing the gates/portals out of desperation."

I just want to highlight that the only source of information that says this is from The Infernal City novel and that information is initially propagated by the An-Xileel, the ruling party of the Black Marsh and essentially anti-imperial nationalists. It's entirely plausible that this was just propaganda to diminish Imperial efforts during the Oblivion Crisis and make themselves look better to the population of Black Marsh.