Or...or...get this, guys.
KHIII is just badly handled in plenty of fronts. Most of the complaints here are from that game. It's a mess. Whatever fucks Nomura gave left with this entry.
To be fair, however, the Organization members this time felt like they've been juiced up (Larxene was able to built an ice maze) for whatever reason that we haven't been given any explanation for, so there might something else at work here. And Aqua was suffering from "PTSD". Make of that what you will.
Also, we don't know how the Kairi battle ends up. Just because we can play as her doesn't mean she's able to defeat him (i.e. Leon, Sephiroth, Cloud). And if she does, well, that's KHIII for you.
Technically, Roxas was throwing an emotional tantrum at the time and was thinking less with his head and more with his anger. In any other fight, this is a grave disadvantage because your opponent can outsmart you while you're simply raging.