He lost because in Arena, most stats and overall BP dont mean squat. Outside of Arena, that fight could have potentially went the complete opposite direction. You need to remember that Arena makes the fight pretty much level, where overwhelming BP is no longer a factor. Your team has heals, and your Earth Main was probably buffing your team with shields. His team has no heals. And that Naruto isn't even that good. One team with heals in arena, has a good shot versus a team with no heals.