I don't play LoL that often, so I'm not a great player, and when I do play I tend to like supports the best. I looked at yuumi and went; "This hero can help the ADC and isn't very technically demanding." That sounds like a good addition to my roster. Then I looked at her basic statistics and saw the less than 40% winrate. Now I'm not so sure about that.
Is she harder than I'm giving her credit for? I might not be the greatest player, but I do actually want to help out my ADC and try to win.