Maybe, but that introduces some serious problems: notably, had Kuvira four metalbenders in the room instead of two (perfectly obvious measure, considering the importance of the power source), she would have won.

She is not a great threat right now, but she may become one if she masters the Avatar State again, and Kuvira is not the type of person to leave a significant threat to her power alone.

They didn't have much of a choice. Baatar would never break, and even if he did, it probably wouldn't be enough. Their idea had almost no chance of success, but at least it could maybe possibly delay Kuvira a tiny amount of time.

They didn't know she had a way to locate their radio signal inside a large city full of skyscrapers (it's some very impressive tech for LoK).

Your argument boils down to "Beifongs >>> Everyone else."

Korra still is the Avatar. Remember, she has once transformed into a Giant Blue Spirit-y Thing (TM). Kuvira has all the reasons in the world to want Korra dead.

Yep. Kuvira has an excellent understanding of dramatics, and that's the key thing to be a great villain. You can't just death threat someone, you have to it with style. And betraying your boyfriend is lame. Betraying it while standing at attention and shooting a giant noisy cannon? Cool!

That's exactly what I said in my post. The conventional military tech of today (or even the one from WW1) would be able to destroy the mech, mainly because it doesn't have any indirect fire capabilities, and so it's range is not that good compared to normal artillery.

Yes, you're right. Go ahead, Korra, and use the tiny needles.

It can't be too heavily armored. If it was, it wouldn't be able to move through normal terrain. By simple analogy to the normal mechas it wouldn't be able to handle a naval cannon shot…

This doesn't matter. Crush or not, she was his partner. Having her killed was a tremendous blow.

The fact that nobody in the room saw it coming makes me think they're all a little blind. Kuvira is quite transparent in her lack of emotional attachment.

Torturing Baatar Jr would have resulted in:
1- Lies.
2- "Turns out there is no secret weakness to the design. I mean, if I knew it had a weakness, I would have fixed it."

It would be much more of an interesting moment had Baatar Jr manned up and sacrificed himself for the cause. He didn't, and thus he became a foolish idiot, while Kuvira became a stereotypical cartoon villain.

She seems quite rational, even successfully so.

Neutralizing the mobility of a giant mecha should be a piece of cake. One shot from a cannon… oops.