This caused some jarring changes in tone and plot that upset many viewers and prevented the show from having tighter plot resolution. It started out as a mystery show in season 1 with only a few of the answers plotted out.
You’re certainly right that
LOST was not mapped out from start to finish in the beginning. As with Tolkien’s
Lord of the Rings, “the tale grew with the telling.” I think the flaw in your analysis, though, is that it was
never a “mystery show.” Seriously, how many “mysteries” were answered in season one? Very few were even introduced, compared to later seasons. How many episodes focused on the mysteries? Many season one episodes - like House of the Rising Sun, The Moth, Confidence Man - didn’t include the mysteries
at all.
I’m not saying the island was not important. It certainly was. Rather, I’m saying that exhaustive
answers were never important.
The only “changes in tone and plot” that I even noticed were when we started to get
more answers in later seasons. Other than that, the structure remained the same: characters experience island mysteries and crisis situations in which they have to learn to live and work together, while flashbacks or flashforwards (or flashsideways, in the last season) illuminate different aspects of the character development by juxtaposing different time periods in a character’s life.
None of that ever changed. It remained eminently consistent.
The series creators simply sprinkled awesome mysteries into the story that sound cool initially, but had no basis for how to resolve the mysteries in the grand architecture of the show . . . The show attempted to fly by the seat of its pants, and just couldn’t quite manage to deliver a griping **and **cohesive plot arc.
(a) The only “awesome mysteries” that weren’t resolved were rather minor ones whose thematic relevance had already worn thin. An article linked to on the previous page was titled, “More Important Than Polar Bears” - meaning, of course, that the show’s characters and its treatment of the great human and spiritual mysteries were more important than a thorough explanation of Tunisia, the polar bears, time travel, etc. - all of which received their due (which was not a lot).
(b) And actually, the
big mysteries - Jacob, the light, the Others -
did receive full closure in a way that formed a “cohesive plot arc.” For instance, Jacob and his brother’s story was all about the human potential for corruption, and how far it goes. The light, Jacob’s “mother” explained, is inside every human, but if we’re greedy and try to seize more of it, we “could put it out,” which is why it needs to be protected. Notice that Jack and the main characters were able to be engulfed by the light at the end, once they had learned to “let go” of what was holding them back from goodness rather than clinging to selfish desires. They surrendered themselves to self-sacrifice - they
didn’t seek the light, and so they got to enjoy it. This is reminiscent of Christ’s claim that “whoever loses his life for my sake will gain it, but whoever seeks his own life will lose it.”
In this way - and this is just one example - the major mysteries
were both relevant and connected to the character development, thus unifying the plot-based mysteries and the characterization far more closely than people tend to realize.
I find it best not to talk about it at all. As soon as I start talking about it, I know I’ll say more than I should. 
I think you could definitely say Jack was a “type” of Christ. There’s a difference between typology and allegory. Allegory is more of a one-to-one correlation (i.e. Aslan = Christ in Narnia) Typology is not like this. A character can be like Christ without actually being Christ. In Scripture, many of the OT heroes are types of Christ, even though they obviously have their faults. Lord of the Rings is similar with Frodo, Aragorn, and Gandalf all being types of Christ.