I definitely don't remember hearing anyone use multiple timelines to explain all that!

"Didn't we learn from Mrs. Hawking that whenever there are variations in time, the universe (or the island?) corrects them? So it goes to reason that any multiple timelines will end up being "squeezed" together into one, eventually.

"So multiple timelines can't really exist. When something new happens in the past, that new thing is not going to make any difference in the end. Timelines come together, not split. An action doesn't result in two planes, two Jacks, etc. Assuming we believe Mrs. Hawking. And why not? She's a sweet old lady."

I think you don't understand the multiple timelines theory. Timelines don't split, true but they also don't come together. In fact, they have no effect on each other. Multiple timelines does not go against what Mrs. Hawking was saying. But if someone crossed over from one to another, that would be a problem and it seems to be prevented somehow in the show.

The idea is attached to some very real and exciting science so I don't find it boring at all.