Well, first off, we know that we get double the damage off of Arcane Comet instead of Summon Aery. We cannot get an exact number since he gives us no gear. However, by looking at your guide, we can get an approximate number for what you would get out of it using your example build. about 20.5 for Summon Aery and 46 for Arcane Comet (At max level). However, since Summon Aery has a much lower cooldown than Arcane Comet, we get more aery shots than comet shots, and are limited by the cooldown of your general poke ability Volley instead of the cooldown of Arcane Comet. Therefore, I would triple the value of the aery damage to 61.5 for a closer amount of damage. Therefore, both do about the same, however the difference is that one is a targeting spell, so you are guarenteed to hit while comet is a dodgeable AOE. Since slows are applied with Volley, you are pretty much guarenteed to hit Arcane Comet, however, there are less time it will be launched, but the upside is that it can hit multiple champs which would then double the damage. The final downside to Arcane Comet would be it last hits minions. Hope that analysis is helpful.