You can't count on winrate when assessing Ashe, she's an adc that plays very differently than others. In a way, you could say she plays a "supporting-adc" role. Ashe is much better when the team are organised, like in 5v5 premades for instance. This leads her to being weaker in SoloQ where coordination is ... welll, soloQ.
Also there's a lot of people who try to play her as any other adc, even though her playstyle is more methodical and rigid. She doesn't have the draven trades, not lucian's mobility, not xayiah's escape potential or set-up and burst, ... but she has utility. Slows everywhere, a vision giving ability and a long range stun-engage. But it's not flashy, there is little montage potential. Ashe isn't a bad champion, it mostly feels like it when you aren't used to her gameplay.