I do think your harder on the game then it really deserves. First of all, a lot of the paradoxes really are paradoxes. A paradox is defined as a thing that should not exist/happen by the laws of mathematics/physics/reality. Many of the paradoxes were self-creating loops: things that existed because they had come back and created themselves. You can't get much more paradoxical than that.
Personally, I'm glad they turned their back on FFXIII. FFXIII had good atmosphere and character potential, but I thought its plot was FAR worse, and took itself way too seriously for what it was. FFXIII-2 has a lightness to it that could kind of play with itself, despite it's flaws. I'll more easily forgive any flawed plot that knows that its flawed, and has fun with itself.
And by a character aspect, as we've already discussed, FFXIII made a lot of bad design decisions (particularly Snow/Serah) that it's good to see SE trying to revise. Some of the changes aren't accounted for, and those are usually the ones that are more forgivable in the first place. The rest of the changes they usually give pretty decent reasons for. Lightning became a knight because she basically had to. She was whisked away to a place where a madman was both trying to destroy everything, and kill her personally. She's fighting for her life just as much as she's fighting for any overarching goal.