I doubt he learned his lesson in that sense. By KH2, we already had Namine, and we were introduced Olette, but that didn't stop Kairi from crushing and burning worst in KH2 (And CoM in a sense) than she did in KH1. It's her problem alone, not in the series, which is why I say Disney's to blame - had it not been for them, they could've either done something useful with Kairi from the get go, or hopefully wouldn't have felt such a need to throw her in as Sora and Riku's failing yaoi shield.