Yeah but Bo Katan didn’t win the darksaber from someone through combat, yet she had no problem claiming it. Now all of a sudden, she can’t accept it? Doesn’t make sense to me.
Well, that’s kinda my point, if Sabine didn’t have a proper claim on it then why not simply take it. Din on the other hand has a proper claim to it now. There’s also the possibility that she failed to unite Mandalore because she didn’t have a proper claim to it and the Mandalorians rejected her as a leader, hence why it was so important for her that she defeated Gideon. The important thing to me though, is that this adds some interesting drama for the next season and it makes sense for this series. All other lore details can easily be explained away the same way The Children of the Watch explained the helmet rule.