I disagree.

Many of the manga-based anime were produced in parallel with the manga, so they would need those filler episodes to kill time. They were also adapting a fixed media with iconic images, so frozen poses of each character reacting to something "needed" to be included. Same thing with freeze-frame fight sequences, or extended power-up poses. That sort of filler could stretch a single chapter into three or four episodes. And then sometimes they would just make up some crazy shit for a few episodes. Oh no, the heroes have to fight a dinosaur somewhy.

With Avatar, there was no manga, and no need to fill time. The episodes were planned as part of the series, written and storyboarded for television.

Maybe the pacing wasn't always great, and there are some less exciting episodes. Appa was lost for way too long. But that's not the same sort of filler problem that anime struggles with.