Actually from what I remember a lot of moves from Roxas are similar to Sora's own in both Kingdom Hearts 1 and 2. I played them both. And I'm pretty sure that Kingdom Hearts 1 Sora doesn't have some of Days' Roxas moves. But that's not why I joined this thread. I actually came here to discuss Kingdom Hearts 2 Final Mix Roxas. I mean the boss battle Roxas. I'm not sure if you didn't mention him because he only appeared on Final Mix or if you truly believe that VALOR form Sora is basically the same. If you do, well, then I'm afraid I disagree. Unlike Valor form Sora, who can't use magic at all, Final Mix Roxas COULD use magic, and he did, quite awesomely in fact! I can't really remember any Keyblade weilder that used Light magic like he did. I dare say he was much more skilled than say, Sora, using Light magic. But that may just be my opinion.
Your analysis were pretty good. I would like to read what you think of this Roxas, and the reason for the extreme changes in his fighting style.
Edit. I just realized how old this thread actually is... oops.