These two abilities are used similarly, but HM got hit to CD 3 while KB got buffed to CD 1. Who made this flub?
Both abilities are unique and deserve to be separate abilities. Knocking someone up against a wall or Poison Cloud is always fun. Also Knockback can be used for psuedo AP generation by knocking enemies closer to one of you other champs etc. Knockback can also be used to disengage one of your champions etc. Hinder movement just slows and damages champs down.