You missed something very important about the finale: Kylo Ren at the end does not become the Johnson/Jung balance he seems to offer to Rey. He seems to believe that by tearing down everything from his past he will achieve this perfect balance. But perfect balance in Star Wars is extremely difficult, and Ren definitely does not reach that balance. In fact, he lets the darkness completely consume him, whether he realizes it or not.
In Star Wars, the Dark Side is the corruption of the Force. However, the history of the galaxy far far away shows that this corruption is less of a spectrum and far more of a circle. As seen in the Prequels, extreme light where the dark is surpressed like in Jung's model leads to arrogance. Extreme light, in this way, corrupts itself through the arrogance of the Jedi. All this brings everything back to Darkness, hidden beneath the light. Therefore, prophecy of the Chosen One is definitely true, in that before Anakin, the Force is unbalanced. Not in a sense that the light has surpressed the darkness, but the darkness has creeped in. The shroud of the dark side, as Yoda puts it. The state of the Jedi Order in the Prequels is what led to Palpatine's arrival, and destruction of the Republic and the Jedi Order. Anakin, following the prophecy, must reset everything by destroying the arrogant Jedi, then destroying the completely evil Sith. This happens through all 6 initial Star Wars films.
Following this, what needed to be done was for Luke to bring a synthesis. And that is what was implied at the end of Return of the Jedi: Luke's darkness within does not define him. He is still a Jedi. It was implied that Luke accepted the darkness within him but did not allow himself to completely turn. What The Force Awakens and The Last Jedi implied, however, was that when the light returned, everything returned back to how things were in the Prequels: Suppression of the darkness. That is what happened to Luke: Though he seemed to accept his darkness, he merely surpressed it. He thought the Jedi of the past, romanticized by many, held the truth about how to truly rid one's self of darkness. His new order followed the same flawed principles of the Jedi of the past: Suppression instead of learning how to control it. That is exactly why his darkness crept back to haunt him and ruined everything when he sensed the darkness within Ren. He doesn't know how to control it, he only suppresses it, but obviously, not enough. It backfires, and in turn, the suppressed darkness returns once again, and we're back to how things were in the original trilogy.
BUT, this all does not mean that the past is completely worthless. That threshold of darkness is where Luke was almost about to fall, and Kylo most certainly fell into. Back to arrogance, back to thinking all the answers are within yourself. Kylo Ren represents the rejection of everything, yet falling into the same trap of the system. DJ realizes this, he's inevitably part of the system, belongs to no one and everyone, and he is content with using this to his advantage as much as possible. In fact, this is his own twisted way of balance. Kylo Ren doesn't realize this. He thinks he has reached true balance and yet he has fallen into darkness.
So what does Rey represent? Rey always believed that the Jedi were good. When Luke said otherwise, Rey still didn't give up hope. Rey represents the exact synthesis that the past suppression always couldn't reach. So when Kylo offers freedom from the past shackles, the system, Rey knows this is a trap. She knows that true freedom comes when bringing a synthesis of the strengths of the past and strengths of the future: Accepting the darkness, learning to conform it, and using it for the best.