Fiora lacks cc or a proper escape. She's a melee attack damage carry, so she doesn't really fit into a team comp all that well. In lower elos, she can carry hard, but in higher tiers of play you need champions that excel in teamfights (as in helping your team as well as dealing damage).
Sona could use a rework. Like, I love her, but she got nerfed so many times in season 4 it was apparent that something needed to be done. She's heavily aa reliant for a support, and her Q doesn't really allow for counterplay. I feel like her passive and her Q could be reworked so her W and maybe ultimate could be changed to be a bit stronger or fitting for her role.
Lee Sin could use a rework. He identity should remain, but his kit is overloaded (but not quite overpowered).