Sej is decent. I'm using her as a comparison point for a few reasons.
1. She was one of the similar junglers listed as competition. She has a couple notable similarities such as using % max health damage for clearing, bringing an AoE disruption ult, etc.
2. I have a lot of recent experience on her, and Kook's aware of that.
Tank junglers in general are suffering a bit at the moment since Riot has decided for some reason to focus more on carry junglers, but they definitely work. Gragas bridges the gap a bit.
I wasn't trying to say he works by comparing him to something terrible. I was commenting on what was actually being discussed at the time.