One thing I was glad about in the DS9 novels was how they dealt with the 'time jump' (was it 3 years, I forget, maybe that was the NF time jump?). At first, it was a bit jarring, and they were talking about things that happened like the kidnapping and Sisko and Kasidy Yates' separating. But I was glad they filled in some of that back story. And they did it in such a way that was organic to the story, and just wasn't a 'this is what you missed...' segment. And yeah, I imagine at least some of those hanging threads might be dealt with in Coda.
I've felt the same way. It's been a long time since I did a relaunch re-read (maybe that'll be a project, now that it's a contained unit with a beginning, middle, and end), but after reading the books and seeing how integrated the flashbacks were into the present-day post-Destiny (and post-Fall) storylines, I thought the whole thing probably wouldn't have seemed so slapdash if the books had come out at the same pace as the early DS9 relaunch, instead of spread out over years and years and those blanks were filled in sooner. Though, come to think of it, there were at least six or seven DS9-featuring books (if not DS9 by title) between "The Soul Key" and when "Sacraments of Fire" started filling in the missing period. Even more if you count stories just featuring the Aventine but no one else from the station.
Speaking of NF, that was one thing that I felt hurt NF a bit, the time jump with no exposition. Just, it's 3 years later (or however long it was) and everything was different and almost no explanation of what happened. Suddenly Shelby is an admiral, Calhoun and Jellico are besties and various other changes and just no exposition at all. I found it jarring and at least for me personally NF was never the same for me after that.
I agree that NF never recovered from the time-jump and would recommend anyone reading it for the first time to consider "Stone and Anvil" to be the "series finale," but that disorienting effect was the entire rationale for doing the time jump. PAD (and John Ordover? Was he still editing NF at that point?) was very clear in interviews that the reason for the time-skip was the idea that, when New Frontier started, all the characters had unplumbed backstories and hidden agendas and secrets, but by the time we'd gotten to S&A, everyone and everything had been pretty well established. The time skip was meant to shake things up, give the readers new mysteries and questions about what was going on so the series wouldn't get stale and episodic. I don't really think it was successful in that (well, I think the entire concept was flawed and it was a bad idea to try and roll back the clock on a successful series having matured into a new phase of storytelling after its initial installments). I've seen attempts to do similar things work out better; the TV series "Defiance," for instance, radically altered its status quo every season, usually with an accompanying time-skip of a few months or so, but in those cases, it was usually skipping over fairly straightforward developments from the previous shocking season finale, and not upending things in ways that were intended to be apparently inexplicable so the audience would be invested in demanding some sort of explanation for what had happened.