Legend of Korra

I think it's more the fact that she could bend without using her arms- so extremely precise and psychically manipulating things that would normally take significantly more effort than what she was exerting.

firebenders can breathe fire. not impressive.
toph being able to see with earth bending is the closest thing i can equate that woman's bending too: highly specialized and situational brought about for their unique requirements. Sure bae fong learned to use it as well, but she wanted to impress her mother, so her motivations weren't as impressive as "well, I'm blind, but Ima use earth bending as sonar / oh i have no arms! woe is me-- just kidding ima make water tentacles.
Look at Katara in the first series, she made tentacle arms out of water bending in the FIRST SEASON. Still not impressed, and that water bending octopus lady was, to me, the most underwhelming of the villains because of that.