He did say that, but for what reason it's not clear, it's one of those bad inconsistencies about the show. Because at the end of the season when they didn't press the button the Island almost collapsed in on itself. Desmond's not pushing of the button caused the plane to crash even.
I can see where you're coming from though. They've certainly simplified alot of things we originally guessed would have extremely complex answers. I still think alot of the themes that made the show interesting are still present, but the show probably won't end as densely as I would've preferred.
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