The difference is that Pearl's fuckups stick with her within the story, and Korra's fuckups stick with her without the story.
Pearl is an internally consistent fuckup who actually has a lot of moments of personal success and triumph. She started from a place where the viewer believes she's the competent professional she presents herself as, and it's during the course of the program that the cracks start to slowly show, before shattering into the emotional catastrophe she really is.
Korra by contrast looks cool for precisely one half of an episode before she's shown to be kind of a retard, and just never seems to move from that point. Every epiphany and lesson learned in one season is forgotten in the next, and consistently the only way the conflicts of the season are resolved are last minute ass-pulls or "Gut feelings" that lead to a nice clean wrap up.
Steven universe gets a lot of hate around here, and the human garbage-bins over in /sug/ have more than earned that reception, but SU remains an objectively better written, directed, and executing series that Korra was, even at its peak in season 3.