I mean I guess. But that's not really how story works. You really need some kind of arc or follow through. So while yeah, I can step back and say, okay Korra has learned compassion. Fine. That's great. As an overall character/series plot point, that shows she's grown.
But when you have like NOTHING really building up to that. At best, you have her questioning why others are doing this to her (what you pointed out). But there still was never like, a moment where she questioned these things (in the sense of, having an issue of forgiving. Her issue was accepting her abuse, accepting it happened to her, and then moving past it. That was the crux of her entire dilemma. NOT that she couldn't forgive the people that did these things to her. At least, that's how the story was shown to the audience. If that was not the intention, I feel they did a bad job communicating it. But to me, the plot was about accepting the bad things that happened to her, and also struggling to find her relevancy because of these bad things were a reflection of the overall world finding less of a role for her. So it was more a personal struggle to find her own self and role. And letting go of the bad things people did to her).
So while I can agree with what you are saying about it being a positive plot point that does reflect on Korra overall. It doesn't work for me, when I feel the finale itself really didn't do anything with the character or story. I felt the finale itself, was lacking resolution, pay off etc. It was lacking it from a season point of view (the season arc). And it was lacking it in terms of, any plot from the overall series (and how the character got to this point) being brought to a close.
Yes, that moment was great. But it wasn't a band-aid fix all, for everything else.
EDIT: This post was kind of sloppy. I guess my issue with the suffer for compassion line, is that they didn't really build up to it in Book 4 (and I don't really think it was built up anywhere tbh. But that's just me). But I suppose while I think it's a great moment, I still take issue with the writers not dealing with Korras other arcs, or having that kind of pay off. Because while yeah this moment was nice, I think it does lose some of the emotional impact, when you don't have that journey that supports it. Of course, if you think the overall series supports this moment, then you probably loved it more.