In my low experience, I would say to go with the fire team, for multiple reasons:
-The elemental advantage is not even close to help with the huge power gap between the two teams. 50% more power is really big, even if you had no eidolon, no assault weapons and no soul weapon, you would still do more damage with the fire damage than with the wind team + elemental advantage. The damage reduction can be useful, however, I believe that you still have much more hp on fire team (and you have a healer with def buffs in the fire team, so...)
-But, of course, you do have both soul weapon, eidolon (both stacks additively with elemental advantage, lowering the comparative advantage it provides) and more assault levels.
-Finally, if you can have a more coherent team with additional tools in fire, added to the advantages above, you should go for it.