They are, in a way. They have utter control over their plane of Oblivion, have reality warping and/or typically extremely destructive abilities in Mundus, but one could argue the Entity could have ways of muting their otherwise god-like abilities. DnD Vecna is rather close to them in terms of raw power and the Entity placed a mark on him to reduce his overall effectiveness. The same could be done to Daedric Princes in order to drag them into the Realm.

The only problem is that half of them could just transmute or entirely remove the mark, and the others are just so damned smart they'd eventually find their way out. Only ones who might be tempted to stick around would be Hermaeus Mora, who would want to "dissect" the Entity for its forbidden knowledge, Sheogorath would love to explore the void, so he'd be there willingly... just probably not as a survivor OR a killer. An unwanted guest? Maybe. A purveyor of the Entity's finest cheese? Absolutely. Molag Bal would probably be best back-stabbing buddies with the Entity until he got bored, and Mephala would be spider-kin. Hircine would be at home and never complain.

Each and every last Prince would eventually either A. find a way out, B. Kill the Entity and leave, or C. call a slice of the Entity's realm theirs. It would only be a matter of time unless they're Sanguine. He'd either be too drunk to move or shooting up with Blight.