Hail of blades doesn't reward you for landing all 3 hits
First off I would like to mention that the runepage would be great for caster marksmen (Varus Jhin)
So instead of buying
(no one buys it on Varus or Jhin), I could see them running Hail of Blades simply for Ravenous Hunter and sustain through lane that way. (Since they will lack healing from kills/assists, and have no fleet footwork)
And the main sub for "caster marksmen" tends to be sorcery sub for more damage off Varus Q's and such. (MF ultimates)
Hail of Blades After landing 3 basic attacks your character's next skill shot ignores armor and magic resist.