Yoshi

I don't consider these moments comparable. Korra just happened to be able to airbend in that moment, changing nothing about herself to accomplish it. Yes, she'd lost her bending, but she wasn't struggling with airbending due to overreliance of the other elements, she was just bad at airbending mentality. I'd argue she airbent by complete accident since it looks like she was trying to firebend. Bolin had no reason to believe he was a lavabender, he just tried it because it was either do that or die. Luckily, he happened to have that talent; zero training necessary. Katara had spent the past few days learning everything she needed to in order to be a bloodbender. She's only doing it for the first time in that scene because she was recently taught the final steps and Hama backed her into a corner. Before TLoK retconned it, any earthbender could potentially metalbend, but Toph was in a unique position to figure out how since she mastered seismic sense. She had to use what she already knew about earthbending to manipulate it to her advantage. Bolin and Korra were given powers while Katara and Toph had to earn them. Katara instantly learning water-healing would be a more comparable moment.