Although the Prophets were really the Dominion's ultimate obstacle to properly consolidate the enslavement of half the Milky Way's nations, but how would they also cope with a borderline Type III civilization like the First Federation and the sublimed Organians? Anyway, what happened to the First Federation after that TOS episode anyway?! They easily seemed to be comparable to the Borg Collective or the Voth in technological capabilities, while the Organians displayed similar cosmic powers to the Q - they would probably step in on the Dominion if the Dominion got too far in its cruelty.