I think Fighting-types became more popular because Gligar and Missy are gone, and then Taillow rose as a way to revenge kill Scraggy even at +1 Spe. So Taillow rose as a result of Fighting-types rising. I don't see why people are using Taillow more than Doduo, though. U-turn and Guts are great, but Doduo has more natural power. And activating Guts takes some prediction.