With all due respect to kilobyte, I don't think he has a clear and unbiased perspective here. Tornado is not remotely appropriately balanced, and it would still be incredibly powerful even with substantial reductions across the board. There's no drawback to simply leaving it running, save the possibility of eventually running out of enemies to kill with it, and there's no tactical situation where it won't be useful. It's still incredibly damaging even in a 2-tile wide hallway. You can freely maneuver while using it, fight in melee with full power if you're a hybrid, and can still snipe key threats with your spells even though they have a modest power reduction.
If it's going to continue being considered a Fire/Ice Storm equivalent, why not give it some analogous drawbacks? Those spells create zones on the map where the player can no longer enter without taking some substantial damage, which reduces the number of options available if something inconvenient comes up. Perhaps the player could be immobile while the Tornado continues, either willingly because the tile they cast from is the only non-damaging tile nearby, or unwillingly because the Tornado ends if they don't keep casting it.
Or perhaps that modest casting penalty while you have Tornado up needs to get a whole lot worse. Spell power isn't all that critical when everything is absolutely wilting around you already, and defensive spells like Haste, Blink, and Deflect Missiles still need to be refreshed during the killing, so perhaps it would be a more meaningful penalty if you simply couldn't cast spells at all while maintaining your Tornado.
Or how about having it cause self-damage no matter what? It's a theme shared with most other air spells, since often to get the best multi-zaps with Shock and Lightning Bolt you have to be willing to let it arc through yourself a time or two, and Static Discharge and Chain Lightning are also notorious sources of uncontrollable self-damage. Occupying the eye deals less damage, but you're still going to be nailed by flying debris.
Galefury wrote:It's not like people can cast it in Lair.
If you play a kenku air elementalist, you absolutely can have Tornado practical by the time you've cleared Orc 4, Lair 8, and located the entry to Vaults. You just need a modest amount of luck with books. I've done it with early access to the Book of the Sky, which allowed me to use Air Strike instead of Lightning Bolt. That same character found Tempests on Orc 4, and could cast Tornado at excellent by stacking Vehumet wizardry with one ring of wizardry. It made Swamp much less tedious, let me tell you.
Galefury wrote:And air alone wont take you through the game, you will need at least some conjurations and charms.
There is no need to train conjurations beyond the early game, and everybody trains charms even if they don't have any synergy with their main combat damage skill.
Galefury wrote:Shatter is another offensive single school level 9 spell. I haven't tried Shatter, but I assume it completely annihilates most branch ends (it goes through walls after all).
It does, but you have to cast it multiple times. Which is probably how it should be.