When picking runes from Sorcery, I never feel good about it afterwards. For most mages, aery and comet are the same thing and Phase Rush isn't really an option. Honestly I don't feel like it matters if I pick aery or comet on most mages. They both do no damage after early game. I forget I even have a keystone once I'm grouping. The keystones are are boring and feel worthless to me.
Sorcerys second line is the only line I'm happy with. Mana flow band and ultimate hat are both good runes. I've had games where I felt like I messed up by taking MFB instead of Ultimate hat and vice versa. Nullifying orb is pretty good too but I wish it was useful against AD assassins.
The 3rd tree is just stats. I just go transcendence because I want CDR. I've used Cerelity and it's ok I guess. Lastly we have Absolute Focus which is an absolute waste of a rune slot. What mages actually want this? When is this rune useful? Seriously I want to know. I won't flame you for making a case for it.
As for the 4th line, I wouldn't miss any of the 3 if they got replaced. The only thing I like about this line is the early/mid/late dynamic it has. The biggest problem with these 3 is that there is nothing fun about them. Late game scaling probably shouldn't be a rune, Waterwalking isn't great because of how the game works. If you lose early you're going to spend all game shoved in and unable to get much use from it, and Scorch can't be good with out being abused by ranged top laners.
The worst part about the Sorcery tree is that even though it's supposed to have been designed for mages, the best users aren't even mages. Sion, Camille, and Miss Fortune get the best use out of arcane comet. Gnar and Jayce use Aery and scorch better than any non enchanter. Phase rush is barely used by mages at all.
The tree needs a serious rework. I would go as far as saying it's the worst tree to take for your primary.