In 16 games in right, kaplar's made 1 error. In 20 games, Millar's made 2. Nixon made 4 errors last year in right field. But that's beside the point.
The RF spot, so far this year, accounts for 3 errors. OH NO! How can you go and blame the sox's defensive woes on a position that has 3/34 of the total errors? The vast majority of errors, on all teams, and especially this Red Sox team come from the infield. Mueller has made 7 errors at 3b. Our 3b defense doesn't suffer without him. It improves. 7 errors in the 34 games he's played is horrible.
Crespo has 2 errors, Bellhorn 2, Youki has made, um, 0 errors in the WHOPPING 2 games he's played. Dauber's made 1 error this season, Ortiz has two errors and Millar 3 (at all positions). That's all for the platers you listed. So, I think the only really REALLY weak defensive spot is Mueller. And he's injured. So that kind of helps us, yes?
Nomar makes a lot of errors at short, and Reese is a defensive upgrade over him. So that injury helps us in the defensive deparment. Sure the team is playing sloppily, but not for the reasons you listed. I'd argue more that the injuries have hurt us offensively, not so much defensively.