I didn't mind the start of it, with Sisko returning for the birth of his daughter. Considering Avery Brooks' own disapproval of the idea of Sisko leaving his pregnant wife and unborn child, it made sense for him to come back for it.
But his portrayal in the DRG post-Destiny DS9 novels never sat right. I see some seeds being planted in Fearful Symmetry/The Soul Key of Sisko being some kind of tool of the Prophets to set certain things in motion, presumably in the expectation of tackling it further in the then-still nascent Ascendants storyline, but then the time jump to after Star Trek Destiny happened and... Sisko did NOT respond like Sisko anymore as far as I could tell. The division of him from his family, from Kasidy in particular, ESPECIALLY, again, after Avery Brooks had expressed his concerns about the optics of a black man abandoning his family... It just did not play as Sisko.
Basically, I think that Sisko, post-Prophets, would not fall back into the standard mold of just another Starfleet captain, and yet that was the version of Sisko that it seemed that DRG had chosen to make him in to, for... whatever reason that never made sense to me.
That said, I'd personally say that it's tied into a bigger "worst non-canon decision" made, and that was DRG being the lead voice in the development of the corner of DS9's ongoing story - I've said before, I feel that he became very focused on the grand plan, making sure that all the pieces were where they needed to be over the course of his writing, but it ended up meaning that the plot was driving the story, while one of DS9's greatest strengths to me was how the CHARACTERS had always driven things, and that just completely tanked a lot of my interest in the developments there, because it didn't feel like the characters mattered, just the way that they were in the right place for the bigger plot. That on top of how it also felt like there was a lot of waiting around for those plot developments to happen, with the characters just standing around, waiting and talking about "well, there's a thing that'll happen, so let's discuss the thing that'll happen so we're ready for when the thing happens and we know how to handle the thing happening when the thing happens."
When there were the occasion side story featuring DS9 developments - Una McCormack's The Missing and Enigma Tales, Jeffery Lang's Force and Motion, even the use of DS9 elements through David Mack's entry in The Fall - it felt more like the familiar developments, because these were stories that had stories centered on the characters and how they responded to the events around them. But the "main" storyline, for lack of a better term, being written and advanced by DRG just felt like novels I was picking up more out of obligation than genuine interest.