[Huzurdaddi]

for the soul contracts, making them give an extra 1-3 devils, when casting the summon devil spell, similer to the ivy crown, would help balance them. Giving 2 extra devils would make them pay off twice as fast, but you would still need a blood income to use them, along with mage time.

I have to say that is a solid suggestion. But it makes devils an abysia only type of thing.