Nonsense. The numbers don't lie, but can be misunderstood.
First and foremost, the two most important skills a MLB team has are hitting and pitching. Defense is well back from those because--wait for it--the best team fielding percentage in MLB is 99% and the worst one is 98%. That difference is miniscule, even though I agree every error can be painful and some even cost games.
When looking at a team's defense, it's better to look at the individual DWAR's of the players. When you do, you find out that our catcher Narvaez, rightfielder Abreu, centerfielder Rafaela, and thirdbaseman Bregman are all well above average. Plus Duran in LF and Story at SS are slightly above average. The two problems are 1b and 2b. Also, did you know that the Sox lead MLB in total chances, putouts, and are 5th in assists? They are also ranked 4th in turning double plays.
I agree the sign stealing was bad, but it's not as though other teams haven't done it, and that certainly includes Pedroia and our Sox. More to the point, MLB looked at the case and determined being banned from MLB for a year was the right punishment. I doubt that Cora has ever bragged about what the Astros did.
Right now the Sox are not 4 games under .500 because of the defense. Hitting and pitching are far and away the most important skills in MLB, and the Sox team ERA is ranked 22d in MLB and the hitting (runs scored) 6th.