I've considered Losing the peace but the description fron the cover makes it sound a but much on the blasted worlds that I'm avoiding.
"But her homeworld, Deneva, one of the planets targeted in the massive Borg invasion, has not. The entire surface has been wiped clean of everything, killing anyone who did not evacuate and rendering the planet uninhabitable. Choudhury is left to wonder whether her family was one of the displaced. Or are they all gone forever?"
Sorry, this just doesn't look like something I'm in the mood for.
Greater than the Sum sounds like it would be more interesting with more on the carbon planets and less (i.e. none) of the Borg.
I'll bet you that if you read them you'll like both of them.
Losing The Peace is no more depressing than TNG was at times (Maquis stuff especially), and is much warmer than you'd think. All three of the front page amazon reviews remark on the sense of optimism there that has been lacking from prior TNG entries; I'm not just making it up.
And I would say the Borg are obviously present but not the focus of GTTS, and it has a lot of the same big-idea sci-fi that Bennett puts in his other books.
That said, I'm telling you, if you want balls-out optimistic let's-go-find-new-shit Star Trek, Voyager is where you should be looking these days. They're remarkably good.
But to the larger point here, I think A Singular Destiny, Losing The Peace, Full Circle, and Unworthy have been head-on attempts to address, work through, or otherwise resolve the very complaints you're bringing up. And you may dislike their methods, though you'd be hard pressed to find a large number of people that disliked any of those four, but your posts were suggesting you thought this was some Big Unresolved Issue with the Trek line, and it really isn't. They knew what they were doing with Destiny, and they immediately jumped into balancing out the obvious imbalances it created.
Really, I think the darkest book published last year was Synthesis. If you enjoyed that, I don't think you'd have much of a complaint about the rest.