McCarthy would have fit very nicely as the third starter.
First the Diamondbacks signing of McCarthy took a pitcher with a very good track record of success pitching against the AL East off of the market this season.
This report from CBS Sports' Boston mentions that McCarthy was 4-0 against the AL East with 2.33 ERA last season. McCarthy was also had a 4-0 record against the AL East in 2011.
Having a pitcher with an 8-0 record in two seasons in the same division that the Red Sox play four tough competitors would have been a very valuable weapon to have.
The other reason and perhaps the most critical point is it also took a very affordable option away from Boston. The contract terms reported by ESPN's Jerry Crasnick seemed extremely reasonable for a third starter.
$15.5 million total for two years? Seems like a bargain and would have given the Sox tremendous flexibility especially in light of the fact that the Sox contract offer to Ryan Dempster was turned down according to this report by ESPN Boston's Gordon Edes.
If I had a choice between the 29-year-old McCarthy signed for two years and $15.5 million or committing more than $25 million to the aging 35-year-old Dempster for the same length of contract, I believe that I would side with McCarthy.
McCarthy seems to have finally come into his own the past two seasons and has started to reach the potential that was first projected for him when he came to the majors with the White Sox in 2005.
He has struggled to fight through shoulder injuries in his career and he is currently recovering from a horrific brain injury suffered while pitching for the Oakland A's during September of last season.
If the head injury is what gave the Red Sox cause for concern, it is certainly understandable, but every indication is that McCarthy will be ready to pitch at the beginning of next season.
As far as Ryan Dempster?
Dempster has a very small track record in the American League, all of it coming last season with the Texas Rangers.
Dempster's numbers with the Rangers don't instill a lot of confidence: 7-3 record with a 5.09 ERA and 1.435 WHIP. Not to criticize Dempster, but I think the Sox need more of a sure thing as their third starter.
Starters are beginning to come off of the board and the Sox need to make sure that they get someone that will impact the 2013 rotation. McCarthy could have been that guy. Doesn't sound like Dempster is going to be that guy.
The Sox had better hope they come away from this offseason with a significant upgrade.
Statistic used from Baseball Reference.