Oh God…
I just realized something!
Almost every villain in Legend of Korra died/was defeated ironically.
Think about it!
Amon wanted to use Hiroshi’s inventions as weapons to rise to power.
And what happened?
Tarrlok used one of Hiroshi’s inventions to kill him (as well as himself):

Unalaq taught Korra how to do the weird glowing spinning light thing that defeats dark spirits.
And what happened?
Korra used that on Unalaq and ended up defeating him:

P’li’s greatest weapon was being able to shoot energy beams.
And what happened?
Her energy beam rebounded off of the metal and…yeah…gross…:

Ghazan was a lavabender.
And what happened?
He died (by his own doing) by falling into lava:

Zaheer forced Korra into the Avatar State.
And what happened?
She was powerful enough to defeat him:

Even Kuvira would have been killed by her own weapon (the spirit energy cannon) if Korra hadn’t saved her!

And I have no idea if this is relevent or not but I think it’s funny that we’ve learned that waterbenders use their opponent’s strengths/weapons against them. And the show about the Avatar who hailed from the Water Tribe is all about how the villain’s strengths/weapons were used against them.