A very key line from this article:
If you want the highest probability to win a World Series, reaching the postseason for multiple years is more important than assembling the best team in any one year.
The importance of 5th starters, backup catchers, and 7th relievers diminish in the postseason. The plucky, 90-win team with no chance to win more games than the $260 million Dodgers during the regular season is no worse than a 2-1 underdog in a playoff series if they can get in.
A team that is a 2-1 favorite in every round of the postseason is still just under 30% to win the World Series.
The Sox traded a good prospect for Lance Lynn, not just based on his Cy Young potential but because of his reliability. Keuchel, while on the downside of his career will still be a good value if he remains reliable.