I met a dude who was Silver a couple of months ago and climbed to very low Diamond on Orisa only.
He probably improved, but I wonder if he would climb as much playing a hero who isn’t as strong as Orisa is right now. As I said, he did improve and he would probably climb on any other hero, but not as much.
Of course not all Orisa mains are “boosted”, but some certainly are boosted to some extent due to her current status.