I can agree with your statement that Ben's 3 major acquisitions were more likely to underperform than are Price and Kimbrel. OTOH, would anyone expect all 3 of them to underperform to the extent that they did? Hanley and Pablo were both worse than replacement level.
Hanley was arguably the best hitter in the free agent market that year, and the Sox were in need of an offensive upgrade. The team had a need, and Ben filled it with the best available free agent option. It's the same thing Dombrowski did this offseason, but with pitching. Even if we expected his defense to be poor, his offense should not have been.
Pablo's signing was not the best move, but even so, to go from a 3.1 WAR player to a -2.0 WAR player at the age of 28 is highly unexpected.
The pitching staff was not expected to be the team's strength. They were expected to be mediocre, with the offense carrying them in most games. Not the plan I would have gone with, but on paper, it should have worked.