That fight is suppose to be challenging, minus the one hit kills.

In the video you don't have your creature active. They can target your creature, rather than you, giving you time to Rush Attack or use a Stun Arrow or Hide in Shadows, etc. Even if they target you, your creature (or a summon) may block an attack if it is in the way.
Running around in full view of all of the DTP probably wasn't helping much, either, and isn't the best strategy even without the damage bug.

I started that fight off with a Splitting Arrow (Way of the Ranger would have helped, if I had known it then), then after a few hits jumped back onto the ground behind that raised section to heal. Two of them ran around either side, with one taking longer than the other, while two concentrated on my creature. Once I took out the first couple (much easier one on one) the other two were not difficult.