i understand that it has relevance to the world at large. the issue is that it has no real relevance to the specific parts of this story. sure, they could mention it, but to what end? just to say "oh, hey, remember how ayra got her revenge on the frays? yeah, we do to." there's no real reason to show any part of that story anymore because the rest of the story has moved on. if they DID put a little scene in there about it, you either hamfist some throw away dialogue (in which case, what's the point?) or you have a legitimate scene devoted to that (in which case, what's the pay off?).
you think people were irritated about showing some little scarred girl talking to davos and taking up screen time?