My theory is that the Laconia bits (and other hints) were a sales pitch: "See how much story there is left to tell?" Plus we needed to see a bit of Laconia to explain where Marco was getting some of his toys from, and where he expected to receive backup when things went sour... not realizing that Duarte always had his own agenda, going after the "gods" behind the ring gate anomalies, and that Marco had always been a means to his ends and no real ally at all. Strange Dogs really could've been a separate miniseries, though, to give it the room and time it needed to do the novella justice...
But, given that they only had six seasons (and were danged lucky to have that), I don't know that they could've found a better place to set the series down, given that there always was a larger arc and there just was never going to be a solid period at the end like there would be in other series unless they'd been promised a full 8-9 year run. There is, after all, a large time jump (about 30 years or so) before Book 7's events, and Babylon's Ashes ends on a mostly upbeat and hopeful tone. If there ever are spin-offs or future series, they really need the core creative team on board again to make it work, and that's lightning I don't know that they'll ever catch again now that the bottle's open. We've already gotten... what, seven, eight years of commitment of them? It's a heck of an ask to rope them back in for more, especially those whose careers seem to be really taking off. (Frankie Adams just filmed something in Australia with Sigourney Weaver, Wes Chatham's dance card seems pretty consistently punched, and the rest surely have other gigs lined up. And that's not even looking into the writers or showrunners...)
As for the books... do try to read through to the end, if possible. Yeah, the pacing's different from the show, and in some ways I do prefer the TV version of events (love how they developed Drummer, for instance), but it's worth it. It really does the whole arc justice (for the most part; a few minor niggles and stray bits here and there, but there always are), and the epilogue adds a nice final note.