Well one reason Sephiroth was hard was you fought him alone so if you get to fight the soldier with the whole party and he can kill all of them faster then Sepiroth can kill Sora alone well than yeah he's a lot stronger than Sephiroth. I only know about one of the organization XIII data fights and thats Demyx's fight, all I know is that he has more life and he summons more than double the water clones, like I saw a picture that showed 30 seconds and 75 water clones. Awsome!