And… I ended up switching Tigraki Warrior on top when grinding at last stage. Despite pretty weak enemies team, their endless buff could turn things into nightmare. His double skulls damage make the match much faster, which is very helpful.
As for his spell, turned out he could two-shot most troops most of the time. It’s so strong that I think, for the first time, it’s even possible to use 4x Bounty team at stage 20 for maximum 6,000 score. It’s very risky, but very possible. You just have to avoid all enemies’ skulls match, then hope Banshee don’t hit him, and Wraith don’t steal his life.
In retrospect, I kinda regret buying Tier 6 now. I know it’s possible with only Tier 5 and a minor acension orb, but I ran out of it. With Bounty Captain like this, I don’t think I really need him at Mythic to get all rewards. Kinda wish I use @Mithran’s calculation post before deciding to spend gems now.