I didn't think anyone there had it in him to actually torture that guy, specially opal. Kuvira is an idiot though. Why fire the cannon at them at all? She has a gundam, she could have lied, retrieved her to be husband and then still do whatever the fuck she wants. Instead she fired and is not even sure if she hit them. I was kinda expecting someone else to kinda just walking in, slashing out his arm and then begin asking questions (although it seems improbable).
I was surprised that she secretly created the gundam. The thing can be seen from miles away and requires thousands of tons of metal. But then again building it secretly is still more plausible than the gundam itself or the magical logistics and ironclad economy in avatar world. It kinda seems like korra could easily make a tunnel, head right under it and avatarstate-blast it out of existence.
Why hasn't anyone thought of asking the vines for help here? We already know the vines are spirits.
Also, kinda disappointed there was no korra bending this chapter.