NONSENSE

“I like nonsense, it wakes up the brain cells. Fantasy is a necessary ingredient in living; it’s a way of looking at life through the wrong end of a telescope. Which is what I do, and that enables you to laugh at life’s realities." - -  Dr. Seuss

 Let's break this statement down.

Nonsense = Good.

Fantasy = Necessary

Good Fantasy = Necessary Nonsense.

That works well in the crazy Dr. Seuss children's stories.

But on the other hand, Bad Fantasy equals Unnecessary Nonsense.

If one pulled Across the Sea out of Season 6 and made that the pilot episode, then the premise that LOST was an elaborate fantasy world could have made viewing Season 6 more palatable. But it still would not have fully explained The End or the sideways story construction. The more we look at the sideways tangent, the more nonsensical it becomes in the overall picture. 

If the real premise of the show was that "someone" had to protect "something" that in itself creates "life, death and rebirth" (which probably needs no protection per se), the main characters being tossed into the struggle for control of the light cave would equate to a simple classic western tale of sheepherders and ranchers fighting over "water rights"  in the valley. So there is no reason that the main characters had to wind up in some sideways world (but not called heaven)  after death in order to have a happy reunion. Further, despite all the events, deaths, missions, statements about the candidates and Jacob's non-ceremonial power transfer, nothing changed with the light cave itself. 

The whole LOST series did spark heated debates in the fan communities on what things meant, and how things were related, to opinions on the grand purpose of the show. But at a certain point, nonsense does not make good drama.