2) Not addressing the bullpen
As bad as the rotation has been, the Red Sox bullpen has not been any better. From July 1 through August 1, they had an ERA of 5.41. That was the second-worst bullpen ERA in the sport in that span and the worst in the American League.
Since the trade deadline, their bullpen has an ERA of 6.39 … which is also the second-worst in baseball in that span and worst in the American League.
Like with their rotation, they have suffered a slew of injuries, particularly to their good relievers. Garrett Whitlock has appeared in 24 games (including nine starts) and he has an ERA of 3.03 but he spent more than a month on the IL. Matt Barnes (who was an All-Star last year) has struggled and partially due to injury. He has only appeared in 28 games since he was on the IL for more than two months.
So the Red Sox quite literally have the worst rotation and bullpen in the American League since July 1 and what did the Red Sox do to remedy them? They traded away veteran left-handed reliever Jake Diekman to the White Sox.