I understood why this series captured young people the way it did, and why it crossed over for adults, as well. Like many series, I thought the first book was the best.
I understood why my students were appalled by the ending. They want their heroine to live happily ever after. They don't want her to have feet of clay, they don't like ambiguity, they don't want her to survive and quietly settle into the background.
Of course, for middle school, much of the tension, unfortunately, was in the Peeta/Gale choice, and of course many openly or secretly preferred the "bad" boy Gale.
For them, I was able to point out that, unlike most stories for kids, this ending was more realistic. More mature. More shades of gray, although I guess I can't use that expression like that any more, lol.
I see your points, too, although that's not what I was focused on when I read Mockingjay. I think what I was focused on was the near extinction of hope. Not for Katniss, but for humanity. The books seemed to take us through stages, from youthful, energetic idealism to the (inevitable?) tired, hopeless cynicism. It was like my life in dramatic theater.
I was even more surprised to read an interview with the author. I originally compared "Hunger Games" to a meld of "Survivor" and Shirley Jackson's "The Lottery." In that interview, Collins said she was influenced by Theseus and the Minotaur: the annual "sacrifice" of young people set loose in the labyrinth. I saw the connection after she explained it, but I sure didn't get there on my own. I've spent some time speculating, trying to match specifics from the myth to the series, and am left with the tentative conclusion that the connection is only general. I still see more connections to "Survivor" and "The Lottery," to be honest.
In an era of short attention spans, demand for less and less nuance, fewer layers of complexity, and more and more adrenaline-pumping action, both in movies and books, I thought Collins was at least smart about her construction, because it contains both. It was clearly, to me at least, written with the end goal of a film version.
Most of all, though, I liked this series simply because it's NOT "Twilight," and it shifted attention away from that never-ending glorification of stupidity and mediocrity.