I find Tornado to be really useful. I don't use it every fight, but there's no better way to clear a path (it's movement is not entirely impredictable, it's quite broad actually), also removes several status effects including invisibility... The only annoying thing about it is that you can't aim it through clouds. I mean, WHAT?? That's what I would change about it. If you're in a cloud, you'll end up summoning a mini tornado that lasts half a second and clears the cloud above your head. AWFUL. That and reduce its cooldown for at least 3 turns

But it doesn't need to do damage, Aero is mostly a manipulation school (like Hydro). The most efficent school in manipulating surfaces, clouds and positioning imo... If tornado did damage, it wouldn't be nearly as useful, in fact it would be too niche and you would have to worry about damaging and stunning allies...