Chronologically, yes, because it's set at the end of the calendar year and ends with a cliffhanger, as with most Trek season finales of that era.
But the point is that either "season" model is equally arbitrary and an equally poor fit to what the novels actually were, because Marco wanted the books to be books, not just copies of TV shows. His whole goal was to embrace the ways that DS9 in novels could be different from DS9 on TV. Which is why I detest the whole "Season 8" nonsense, because I think it disrespects what Marco was trying to achieve.
I have to pretty strongly disagree. I know you're right about how Marco thought of the books and how he wanted them to be, and he how didn't like the "season model" the fans imposed. But as one who has for my own reasons read them and reread them and re-reread them to such an extent that I pretty much know those stories off by heart now, I'd say the books actually follow a season-of-TV model more closely than the DS9 TV show itself ever did.
The DS9 storyline from Avatar to Unity has a very clear beginning middle and end, with consistent themes and character arcs, exactly like a season of genre TV (network TV at least, not so much your modern streaming binge model). The storyline from Unjoined to The Soul Key (what you might call "season 9") is even more so - a remarkable consistency of theme and motif and character arc, I could write a whole dissertation on it.
The DS9 TV show never did that to such an extent - of course it had continuing storylines and longer arcs than any other Star Trek show until Discovery, but to a large extent it was still beholden to the one-episode-at-a-time model of TNG and never did the whole-season-as-one-extended-story thing (basically, a novel for TV) that shows like Buffy, Arrow, Supernatural and Doctor Who have done. The DS9 books, on the other hand, do have that.
Like tomswift says, I don't think it can be convincingly argued that Unity didn't serve the same function that a TV season finale does - if nothing else, they wouldn't have made it the first DS9 hardcover novel in years if they didn't know it was a big conclusion and worth making a big deal out of.
Besides, as much as I respect and thank Marco for everything he did for the Star Trek novel line (I still think it was better under him than it has been under any other subsequent editor), it is the nature of all art that the audience might take away something from it that the creator never intended, and you can't tell the audience they're wrong to do so.
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