I'm not completely caught up on what's going on with DS9, but the main complaint I have about Ro becoming captain is that she seems to be a Kira substitute. Which is pretty ironic. She goes from rebel, to Bajoran military, to Starfleet officer, becomes (kind of) religious and now becomes captain of DS9. Sound familiar? As far as Elias goes, it seems like he become a surplus character once Sisko came back. Elias had an Orb experience, became friends with Opaka, had an adult daughter who was a fairly important character, and was usually the one who was exploring the Gamma Quadrant. With Ben back, most of those roles have been filled. DS9 ended with many of the series regulars going their separate ways, so I don't blame the writers for extending the characters stories in different directions. Life is like that. But at some point things will have changed so much that the characters and situations will be so different from the show that I fell in love with that I will have no interest in reading further. Not there yet, but I 'd be lying if I said my enthusiasm hasn't dimmed quite a bit.
I remember reading somewhere that originally they wanted the actress who played Ro to be in DS9. Perhaps this is just a way for the books to honour that.
She was part of the resistance for a while. Terok Nor novel: Night of the Wolves gives a bit of background on her activity during the occupation as well as the reasons why she left Bajor.