this is just my own little headcanon, but i feel like mack's role in iswm: part 2 was to represent the paradox trying to resolve itself. because he was obviously there to replace mark, the creator of the paradox. so maybe the paradox pulled in a replacement that it deemed more 'competent'; someone who wouldn't create the paradox in the first place. someone like mack.

the downfall of that attempted solution was that the captain still existed, was aware of the fact that this wasn't their universe, and capable of either erasing mack from existance or allowing him to glitch his way into the worst possible universe (that was something i actually missed on my first playthrough; mack doesn't start out wanting to kill the captain. at first, he's just a control freak. but everytime the universe glitches, he becomes worse. i feel like that almost represents the paradox realizing he's not different enough from mark to resolve it, so instead the paradox starts pulling him in all possible directions to try and resolve itself. it's the paradox desperately looking for a way to fix mark's role in the universe, resulting in it thoroughly fucking up the role of his replacement).