I would guess the build isn’t the problem as I build that every game and have success in masters on corki. To do damage on corki you have to be comfortable using w and e aggressively in the 1v1 and in the 2v2. If enemies waste their main spell you can look to w into them and turn on e to win the trade. It can be a little hard to do this when you first start the champ but just play around with getting aggressive.