Here’s the thing about Korra. It’s not supposed to be compared to Avatar. It takes place in the same world but it’s it’s own story.
The first time I watched Korra, I compared it to Avatar in every way and was so disappointed. I didn’t like the characters or the plot. I recently rewatched it and was amazed at how good it was. Of course it has its flaws like any other show, but it was so much better when I saw it as purposefully different.
I do agree though that the fourth season was definitely the weakest.