Maybe I just don't have a solid memory of the game (I've only played it once when it first came out) but it's weird that so many players lasting impression of Sora in DDD is him being stupid. All of my lasting impressions of Sora from that game were the moments where he showed more emotional depth than usual. The moments that stuck with me were like the scene at the end of Hunchback with him being absorbed into the light (and it's parallel in the ending), or the Friendship is Power scene, or "Aren't you afraid of becoming someone else?" or his stuff with Neku, etc. By the time the game finished those were the Sora moments that I remembered and that stuck with me, but from the sound of it, everyone else's thoughts of Sora in DDD is just "stupid" lol.
IDK. Maybe I'll notice this so-called stupidity more on a replay (hi 2.8) but, yeah, my lasting impression of Sora in DDD was pretty favourable.