Okay, but what if I'm playing a Beast Master or Drakewarden and one of my attacks is from my pet and wouldn't trigger HM? That leaves two attacks, and if one misses than FF and HM are pretty close together. Heck, at higher levels the FF damage die scales so it's ahead in some circumstances.
FF is an optional feature that fits well with certain Ranger builds, for which I'm very thankful. Other builds may still want to use HM, and it still exists for them. This is literally the best of both worlds.