Is There Balance?
Some like to argue that this is not balance. Luke lives, so the light wins. Not exactly.
There are many ways to find balance. Some argue balance is found by numbers. If this were the case, the force would have found balance when Yoda and Luke were the last two Jedi. There were two Jedi and two Sith, but there is a problem with this thinking. If you and a friend are on a basketball court and across from you are LeBron James and Michael Jordan. Is that balance? Do you expect to be able to compete against that team? I think not. Numbers mean nothing.
So what does the balance refer to? The only thing it can – power. Sidious and Vader were fully trained Sith with lifetimes of knowledge at their disposal. Post order 66, there were no Jedi in any combination that could successfully oppose them.
What was achieved upon the death of Anakin Skywalker was the balance of power of both the light and dark sides. Luke may live and may call himself a Jedi, but what does he really know? He knows some fighting. He knows force choke and Jedi mind tricks, but that does not equal a Jedi. At this point there was also no one to really teach him. The force ghosts had limitations in legends. In canon what they can and cannot do is still a bit of a mystery.
Emptiness Is Balance
At that moment both light and dark lacked both trained warriors and teachers. Knowledge was out there and others could learn, but neither side had an organized, learned following.
Remember at this time Ahsoka is out there somewhere. Snoke existed somewhere, probably in the unknown regions. There were also other force users as well, so at no point does balance mean there were no more force users in the galaxy.
Moving Forward from The Chosen One
At that point the force achieved balance and the prophecy was fulfilled; However, the story may be incomplete. Given the prophecy we learned on p. 288 of Claudia Gray’s book as well as the shocking revelation from Star Wars Celebration, everything said may yet change.
Claudia Gray gave us the following two prophecies from her latest book:
“The danger of the past is not past, but sleeps in an egg. When the egg cracks, it will threaten the galaxy entire.”
“He who learns to conquer death will through his greatest student live again.”
Since we know that Sidious will indeed return for Episode IX, these prophecies may change things as we understand them, but until then things stand as is. Also, remember this. A prophecy fulfilled once, may be fulfilled again.