I honestly stopped caring if it was Jack's personal version or not. The whole ending was, as you say, ridiculous if you take the entire series into account. There were so many flaws along the way that seemed like both pandering to fanservice and simple laziness on the part of the writers (like most of season 5) and part of me hates that they went the route of gratuitously killing off so many people, although it was bound to happen, and the things they chose to answer versus what they chose not to answer appear to be huge glaring things, and I'm just so soured on the show because of the last couple seasons. It's a shame, because I loved it until then.

I agree with almost everything you've said, and I believe you have a much better grasp on Kate's full characterization than I do. I hate that the writers made me so bitter about all of it before its time. Most of all, I hate that I stopped caring so far before the end of the series. Watching the last season and a half was, for me, only an exercise in completing something I'd started and that's the biggest shame of all for me personally about the show.