“I once thought that there were no second acts in American
lives, but there was certainly to be a second act to New York's
boom days,” - - - F. Scott Fitzgerald
The Second Act in anything is not a guarantee.
In the series, the First Act was clear: the elements of surviving a plane crash with no hope of rescue. How would average people cope with extraordinary circumstances? It was like the survivors were thrown back to primitive mankind - - - little technology, hostile environment, dangerous beings surrounding them at night.
The Second Act was more tenuous: "we gotta go back" was Jack's scream to Kate. The idea that the O6 would want to "go back" to the island after they had been rescued defies basic human instincts of self-preservation. There was no real reason to go back. The people they "left behind" were mostly still strangers in a strange land. They had only known each other for a few months. For Jack, he had a life to actually go back to: his mother and his medical practice. Kate had a personal mission: to raise Aaron for Claire. Sayid had lesser bonds with the people left behind on the island. He actually received his dream when he was rescued: Nadia and a new life. Hurley had the least need to go back. He had a family and enough wealth never to work again.
When Nadia was "killed" by Jacob's agency, one would have thought that Sayid's pain would be with him forever. If it was truly real, he would have wound upon reunited with Nadia in the sideways church. But he did not. Once he lost Nadia, he would still have no reason to go back to the island because there was no one there he cared about to save.
Hurley's guilt about The Lie the O6 told was enough to get him back into his "comfort zone," being committed to the mental institution and away from the preying public. His best island friend, Charlie, was already dead. His potential girlfriend, Libby, was also dead. There was nothing to pull Hurley back to the island.
Kate had even less motivation to go back. She "beat" the multiple charges against her. She was accepted as Aaron's mother. She had enough money to live quietly in peace. She never had to run away from any problems. This is what she dreamed about when she was in custody. The idea that she had to go back to the island to "save" Claire was irrational since to the eyes of the O6 survivors, when the island disappeared, everyone on it was dead.
The idea that a few mental jabs, some coaxing language and heart string pulls by Jacob or Widmore would get people who had no reason to go back to the island onto the Ajira plane is perplexing; so much so it calls into doubt whether the O6 story arc was actually real or as the boat in the harbor stated, an Illusion.
The Island's Second Act was more confusion. The time skip by "some" of the Ajira passengers made no physical or logical sense. We were already shown the "longing" by Sun to the loss of Jin, but she saw him blow up on the freighter. There was no evidence that Jin was alive. There was no reason for Sun to leave her baby and go off on a crazy scheme told by a known liar, Ben.
If the whole purpose of the O6 was to reclaim something lost when they left the island, none of the O6 really got what they were searching for except Kate, who allegedly reunited Claire with Aaron after the Ajira plane took off the Hydra Island runway. Jack did not come back to the island for anyone or anything. He came back to die, something he could have accomplished without returning to the island. Hurley came back for nothing. His island actions saved no one. In fact, the returning O6 folk were merely pin balls going back and forth between camps as followers in the convoluted tale of Jacob and MIB. Only Kate and Jack fought MIB in the end. And Sawyer showed up only to escort Kate to the Ajira plane while Jack wandered back to his martyrdom. But even Kate's mission to find Claire was one of an accident. She did not know Claire would be brooding near the runway. So Kate really stumbled to her goal of getting Claire off the island.
So if the first act was all about Jack trying to keep the survivors from killing each other and the second act's only success was Kate getting Claire home, what bearing does that have on the End?
If the Second Act was the pivotal climax to resolve the LOST story, then the LOST story was really only about Kate. That may be hard to swallow that the story was all conceived by Kate as a dreamweaver. But since Kate was the only person to get her wish upon returning to the island - - - she is the Dorothy in this Oz. And if we try to look objectively at the sideways church reunion, it was Kate's wish fulfilled that Claire would be reunited with Aaron. And the undertone is that Kate true feelings toward Jack would make him be with her forever. She did so by giving Jack a room filled of people who acknowledged his leadership and friendship. She took away romantic rivals by putting Sawyer and Juliet together. Kate's real Second Act was finding peace in the after life.