I have proven elsewhere, this is actually “hardcoded” into his fight. He WILL one shot Pet even if not taunted. Regardless of any defensive CDs used or not.
In the combat log, you can clearly see he hits Pet for “exact” same amount as their HP. No overkill, nothing absorbed (if using defensives), it’s literally a flat out one shot damage that equals to their HP.
Working as intended!
I did make a suggestion to avoid having BM Hunters “easy time” on him as some/many falsely assume because of Pet tanking to have him simply ignore any taunt/threat from Pets and NOT one shot them. Obviously that’s fallen onto deaf ears since Devs aren’t interested in tuning the fight for different Specs and would rather have it BROKEN for them.