The Sox were 54-32 on July 5, seemingly headed for 102 wins, but played .500 the rest of the year, so I think you have to grant that some pessimism was warranted.
That said, one of your regular comments all season long was that every team had its weaknesses, and my thought is that Cora is especially good at working around those weaknesses. Bloom helped when he picked up Schwarber and Robles and much later Iglesias, who's sitting out the postseason.
The Sox postseason upswing--taking 4 of 5 games from the Yankees and Rays--is not luck no matter how many times espn and others bring up that ground rule double in the 13th inning of game 3. In fact, right now Cora has the best lineup he's had all season. With Schwarber at 1b, he can even keep his "good outfield" of Dugo, Kike, and Renfroe.
His pitching, however, is less than ideal, what with ERod and Sale crapping out in games 1 and 2. Enter, stage right, Cora's long relievers--no longer Valdez and Richards, but Whitlock and especially Houck and Pivetta, both former starters. The latter two were crucial to the game 2 and game 3 wins.