Its not cruel on horses, Aintree has even had the backing of RSPCA. I no how to ride a horse, which makes me feel like it's not a proper sport as there is skill in it but the oxford english dictionary describes sport as skill based physical activitie as indivaual or as team enjoyed by people.
which horse riding to me only covers a few of those things, the same with darts though the thing they dont have is the physical part but tick all the other boxs.