Close, but "let's make the most of it" sounds like it might imply that creating a need for redemption was a bad idea in the first place, and I don't think it was. It was one way of adding fresh drama, and while this particular way (like almost any individual plot choice) wasn't "necessary," it was interesting (to me). And yes, now that it has been undertaken, I would definitely find followup more satisfying than backtracking.
The Finches have already alluded to different tribes, though it was in the dream sequence:
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"Dessa tried to hold the tribes together." By just having her dream this, I think the Finches implied that there are tribes to dream about, and that these tribes might have differing viewpoints, to some extent. If I were the writer, I'd show that there were shades of difference in attitudes towards men among different tribes (and individuals) but I wouldn't limit the bad behavior to just one tribe (like the Bana); I'd make most if not all of them complicit, at least to some degree. I think some amount of moral ambiguity adds depth (for lack of a better word). I might, though, have the Bana be a hard-core misandrist tribe that follows Donna into exile after she loses to Diana.