First, I'd say that the Kira/Keev part was more like 1/2 the novel than 1/4.
The other portions are setup for the rest of The Fall - new DS9, Bacco, where are the characters now. Their character arcs are more character "a"s right now. The "r" and the "c" come in the later books, so their arcs are over the 5-book miniseries
The reason character arcs were brought up originally is because a claim was made that this was a superb character study. The rebuttal, of course, was to ask how it could be a superb character study if there were no character arcs. You can see that there is no arc here.
The next question was to the story arc. It was argued that this book needn't have a complete story arc of its own, because it was some sort of serial novel
. This was proven wrong by the author's own words in the back-matter. DRGIII said that it is a full novel in a series of full novels, not a serial novel. The only way you can get away with not having a full plot and character arcs of your own is to have a serial novel, because it is then explicit that the full novel has been broken into pieces.
And not every single bit of story is about advancing the plot - not every B-story is incredibly important.
Not every portion of a book has to service the same plot. It would, however, be nice if most of this book serviced any
plot. Now, before you go jumping down my throat for that statement, just think about my previous argument. The novel was missing its story arc. Events occurred, but serviced no plot. They were simply there, taking up pages.
From a literary perspective, this novel was poorly done. Not only did it not have a complete plot, it did not have character arcs, and it set up a hook that it did not payoff on.