The aa +Q+aa combo was butchered in the laning phase because of passive removal and Q base damage nerfs(24 damage at lvl 1-2, even more at lvl 3-6). I know they don't like to revert changes but right now corki loses lane to champs he should win (think of jinx, tristana, twitch).
The removal of the 10% bonus damage was unacceptable, because it was a part of the corki play style since early seasons,I think it could be tweaked to 8% bonus damage, or changed to 10% bonus true damage since it was balanced before with the bortk build. Right now there is no efficient item to buy as 2nd item other than the weird gunblade build. this change would make the TF->bortk build more attractive.
In addition to that , the magic pen build is now useless because of the Q , R base damage nerfs and the removal of Triforce AP. there should be compensation buffs to Q and R AP ratio's for these reasons.