Orianna is really strong imo. My friend plays her a lot and does huge damage with her.
I don't feel like her damage is great. She sacrifices a lot for that utility and range, that's just the way the numbers have to work. If you compare her to a straight damage mage like Annie her numbers fall way behind. With the way the meta works your AP mid is one of the most important roles though, and you need to be capable of doing more with the farm you get. Orianna doesn't scale well at all, which was less of a problem when she had better range to soften targets before direct combat, but it's not that easy now. I probably haven't seen Orianna in the last 50-100 matches I've played. Like, literally at all. I cannot think of any other champion that has been so shunned and forgotten by the community, and she used to show up all the time prior to the nerfs.
Who designed Ahri and which other champs have they done?
Ezreal did. He's designed and co-designed tons of champions. Original Jax, Annie, Amumu, Blitz, Caitlyn, Heimer, Jarvan, Kassadin, Kog'maw, Malzahar, Morgana, Nasus, Nocturne, Singed, Shyvana, Sion, Teemo, Warwick, Trist, Zilean, and a few others.