Must I repeat myself about dual wielding?
Spoiler ShowSora was dual wielding long before KH2. Infact, it was much earlier. Roxas and Sora were both using the Keyblade at the same time during CoM and Days. Now, that is pretty much dual wielding, but more like sharing your second Keyblade with someone else. Much like Riku did with Kairi in KH2. Roxas just gains the ability to completely and permanently dual wield because Xion pushed him to it pretty much. Roxas could already do it, Xion just helped awaken it. The same way Sora needs help through Drive Forms.