The whole idea of Gal Dukat, the Prophets and the Pah Wraiths shows how limited the show was only exploring any concepts in around 20 - 30 sets of one hour shows in seven seasons. Usually, in such shows, drawn from the spiritual beliefs of many in real life, entities such as these are concerned about matters such as real estate but are also abundantly concerned with controlling the ideology of people. Not that they be given money but they be worshipped as gods.
A real explanation of such a concept might have an ongoing and powerful set of believers in the Pah Wraiths that spread through Bajoran society like the commonly believed in Satan worshipping 'Illuminati' perhaps. Although not with de facto power of leadership.
The Pah Wraiths in this show were shown to be committed to evil. They are known to take over bodies, seemingly with sadistic pleasure such as how Kenko tormented Miles and how the Pah Wraiths chose Jake, Sisko's son, as a vessel (who at the end of the show describes being taken over by the Pah Wraiths as feeling that a being was pure evil!)
They are also shown to be fairly powerful on the same level as the 'Prophets'. I think Dukat possessed with the true power of these demonic entities would do a fair amount of damage, but how he would fair against various adversities is up to a writer to decide. If such entities (the Pah Wraiths) exist then other entities of similar power must also, and also the magicks used in the show would likely be more exhaustive than what we have seen, with a history, and considering it is Star Trek this would probably link to other things such as distant Bajoran tribes on other planets etc. For instance, the force always has to win out in Star Wars. Darth Vader cannot be defeated by Hans Solo and a new magic ray gun he has to be fought against by a positive force user.
These are some of my thoughts:
- Q would not be able to intervene because, if I were writing it, there would be a magickal reason why he could not, or at least a magickal reason why if he tried he would have a fight on his hands, not an easy day. Q saving the day does not fit into the mythology of Star Trek Deep Space Nine.
- The Borg, an absolutely devastating enemy by any rational calculation but always taken down to the level lower than the dumbest Clingon for the sake of the show would do the thing that was best for their collective, if they could more quickly and easily assimilate 500 worlds for the same energy it would take to oppose the Pah Wraiths over one planet, they would take the 500. Dukats telekinesis I imagine could destroy whole cubes and the Borg have no metaphysical/ magickal protection to call upon.
- Species 8472 would be easily massacred. Those energy weapons would have little effect on the Pah Wraiths.
I imagine Kes's people would be able to oppose them. But I do not see much standing in the way of Dukat's rampant destruction. Perhaps the entity that Wesley Crusher went to learn spirituality from?
Within the confines of the fictional concept that is the Pah Wraiths they need someone connected to a rival fictional positive spirituality to oppose them.
But the answer is that Sisko could not lose the battle in DS9, it is fiction, a fairy tail. The bad guy cannot win; that's just how it is!