Look, I'm fine with Galio doing damage if he builds AP. But, at 500 AP, his Q deals around 50% max health damage, on top of the initial explosion, which has a .9 ratio. That's clearly overtuned. I have no idea how it made it through the PBE.
Compare it to any comparable ability on another mage. The numbers are just ludicrous.
For instance, let's assume Viktor and Galio are both at 500 AP. A target with 3300 health will take as much damage in 1.5 seconds of Galio's Q as they would standing for 6.5 seconds in Viktor's ultimate. By the time Viktor's ultimate is done dealing damage, Galio has already launched another Q.
Galio's Q should not deal comparable damage to Viktor's entire ultimate. And, for the record, Viktor's ultimate does not need its damage buffed.