True, Claire may have a better relationship with Leon, but in RE:CVX, basically the whole story was about Claire and Chris being reunited (along with the whole Ashford spiel of course), and as you've pointed out, they are siblings. As a little sister, I would go into battle with my brother without thinking about it, whether or not we had the strongest relationship (even though I'm lucky and we're very close). Also, it's a pairing that we haven't seen a lot of, other than the end of CVX. I would like to see them together for an entire game (at least on and off like in RE2 with Leon) because I'm pretty sure you would see an awesome character arc as the Redfields are reunited and go through an entire senerio together, learning more about each other along the way. Their relationship can only get better in my opinion.