I wouldn't worry about this too much until we actually know what the fight entails. It seems like very few fight mechanics are finalized yet, and they are just showing the general arena and some special moves Leviathan 'might' have. All we see is him flop across the screen and attack the tank head-on from the edge. I'm sure there's much, much more. Also, I wouldn't be surprised if you end up fighting a LOT of adds on the ship. It's a super large arena.