The Mill archetype has been held back in Commander by a couple big factors: the decks have more cards to mill from each opposing deck, and the games are rarely as long as youd like them to be
That being said, even in the context of the Death Toll person, this still requires work, so it's not like it's broken or anything
Demonic Pact Conceptually, it feels like top down designs like this are usually a little less reliable than their bottom up counterparts
If it were also immune to Edict effects and had indestructible then perhaps it would be more worth the bother of playing it
As much as it is labelled as a Modern set, it has been aimed at Commander players, and some cards might incidentally see Modern play
I used to play an Akroma, Angel of Wrath in my sideboard as a twist but it got stranded in my hand a surprising amount of times so I tried Rorix as a castable version