1. I really don't see why you would argue that the vision in "Far Beyond the Stars" was sent by the Pagh-wraiths to dispirit Sisko. The entire point of that episode was that he was already demoralized, but that being reminded of the oppression of his ancestors and the value of the freedom he was defending from the Dominion was what re-ignited his spirit. It seems probable to me that this was a vision from the Prophets.
But what was there in that vision that would have served to reignite his spirit? It was a story of failure and frustration that ended in despair. I know that the episode ended with Sisko's spirits raised, but I don't see why that particular story would've been chosen as the way to raise them, when it ended so hopelessly. I've always found that a flaw in the episode. It's a cool format-breaking story about the 1950s and all, but in-universe it was always difficult to see the cause and effect. The fact that the second Benny appearance was explicitly a Pah-wraith trick made the first one make sense to me for the first time, once I considered that maybe they'd both been attempts to break Sisko's spirit and that they'd both failed/backfired.
2. The novel Crucible: McCoy - Provenance of Shadows establishes that there was a real Benny Russell in the mid-20th Century. Of course, the Crucible trilogy is not set in the same continuity as most Treklit novels -- but I personally think there's a reasonable argument to be made that Benny Russell may have existed in the "real" Trekverse and that he may have been given visions of the 24th Century to inspire his writing by the Prophets -- who perhaps deliberately sought to link these two men's lives across the centuries.
I just don't find that convincing. The scenario in FBTS was too allegorical.
Plus it makes the Prophets real jerks, ruining that poor guy's life just so they could send Sisko a cryptic vision they could just as easily have fabricated as a pure illusion.