Thrill of the Hunt does not proc from HA, whether manual cast or the free ones. If you don’t have Buriza or Valla’s equipped, then it’s probably not super effective since the Strafe projectiles will only hit the closest monsters and the rest won’t be slowed.
If you are able to hit any monster with Strafe every 2 seconds or less, they should be perma-slowed.
In general though, if you’re using Ess of Johan, Thrill of the Hunt is probably doing very little for you.