While it did seem a bit strange at first, I thought the Wakana-Sara thing actually reached a pretty nice conclusion after re-reading it. My take on it is that the two of them needed closure above anything else.
Sara had feelings for Wakana, but she moved on and found someone else, which is something that many people do. I would argue it's healthier because it shows that Sara isn't going to just wait around and dwell on the "what if's." You can't really grow as a person if you do that. As for Wakana, she needed to get her true feelings off her chest, even though she knows it won't automatically make her and Sara a couple. But to just say it out loud to the person you like is also the healthier thing to do than just bottle it up and--once again--dwell on the "what if's."
And I thought the hug was more of a way for them to put a nice little bow on top of this particular chapter in their lives. It's meant to show that they have no hard feelings, they said everything that needed to be said, and want to let each other know that they still care for one another as a friend.
As Sarah Paulson once said in the movie Carol, "And then it changed. No one's fault." "It" being "feelings," and it's true: it's no one's fault that feelings change because that's what they naturally do. Wakana and Sara don't feel anything romantic anymore; it's close friendship now. And I think this kind of experience would make them even closer as friends because they were completely honest with each other.