In the end, wasn't Eclipsa kind of a dull character? She ran off with her monster boyfriend and had a baby, and the Powers That Be decided to freeze her, and then she got out. Where's the arc there?
The whole dark magic vs. light magic thing ended up not really mattering. 'Her' darkest spell was actually her mother's, and that whole thing just kind of fizzled out anyway.
If her whole character arc was her learning to take responsibility for her people, this is just me talking, but that's kind of a snoozer. And they didn't really lean into it enough anyway.