I really wonder why no one used air wizard.
Air hasnt had a ton of support to flesh out the school. fire got expanded by 2 warlocks (and an academy warlock now), Earth got fleshed out more with 2 Warlords, Water is only just now being built on in a big way, but Water training has always been high value training because it lets you carry more staple spells like Dissolves (major value), Surging Waves, and Acid Balls.
Fire only added 1 Warlock in an expansion (first Warlock was base set), and it got far more Dark than Fire (probably so as not to benefit the Wizard too much). Yes, Earth got 2 Warlords, which definitely made the Earth Wizard a lot stronger. Water always had Dissolve, but it got a lot stronger as expansions came out: Surging Wave was in Kumanjaro, Acid Ball was in Druid vs Necro, and Crumble was in Academy. I think it was Acid Ball that really tipped the scale towards Water, whereas Fire was probably strongest in the base set and Earth only became playable after Forcemaster vs Warlord.
Air got quite a lot of new cards in Academy: namely Azurean Genie and Lightning Raptor, and lots of attack spells that deal Stagger (Lightning Jolt, Forked Lightning, Piercing Thunderstrike, Voltaic Discharge). And then there are all the (mostly Wind) Air cards in Domination: Windstorm, Sandstorm, Gale Force Ring, Bolt of V'tar. Hopefully we'll get Staff of Storms (promo) in an expansion soon (perhaps Lost Grimoire?). On top of that, the Poison-related cards tend to be in the Air school, allowing an Air Wizard to have cheap access to some DoT cards (and nothing stops a Wizard from playing other DoT like Idol, Plagued, Magebane and Ghoul Rot). Right now that just means Poison Gas Cloud, but I imagine Wall of Poison Gas might come out in the near future. If so, it will help the Necromancer, but could also help an Air Wizard running a non-living "buddy" (could be a Zombie Brute or a Devouring Jelly or whatever). And you can even use Raincloud to mitigate some of the damage to your own living creatures from effects like Idol, Plagued and Poison Gas Cloud.