I asked about the Death Grip trigger in 7.1.5, just something I heard from people testing it. Would be awesome if someone who has tested it replied and confirmed or denied the claim.
Everything else you wrote on the list is true.
https: //www warcraftlogs com/ reports/wZaq3AH4j KNG1fdX#fight=1&type=auras&source=1 9&ability=208052
This is my Guarm mythic kill from last week, you can see that using pet stun will trigger Sephuz even when on the boss (pre 7.1.5 for future reference).