Everyone has a plan at some point... but is there an overarching plan connecting our characters further or are they always bumbling pawns?

Michael seemed to fight hard for Walt, and he was obviously manipulated into giving Walt aged 3 up to Susan and Brian Porter. Since Walt aged 10, Vincent and Michael are missing from Alt 815, does that mean Michael never gets Walt and Vincent in Australia?

Shannon is also missing, having stayed with her boyfriend Brian (Bryan?)

What caused these changes in the flight manifest... are these clues about who was really meant to be on the Island and who was just "extra?"

Exodus Part 2
[We see Michael at a pay phone.]
MICHAEL: ... I can't do this, ma. -- You know, I was -- listen, I was thinking -- I was thinking maybe you could take him. -- Look, ma, if it's a question of money, I... [Locke goes by in his wheelchair] What am I supposed to do with him? He's not supposed to be mine. He was never part of the plan. Yeah, I -- thanks a lot. [He hangs up and turns around to discover Walt standing there.] Hey, man, I was, uh...
WALT: I need new batteries.


In getting Benry back for the Others and Walt back for himself, Michael kills, lies and leaves. Walt ends up with the grandmother who didn't want him above.Was Walt a wrench in Michael's plan or some overarching plan?

I just don't buy that everything rests on a character not truly introduced as more than a judging smoke monster until the last epi of season 5.