Fair enough, let me do some research on this. I compiled a list of GS from each playoff team and AL East team in 2013, excluding the top 6 most frequent starters. I fully understand the flaws in compiling a list in this manner, but as a quick analysis without examining each team's initial five starters at the beginning of the season, it serves its purpose.The Red Sox are pretty much in the middle of the pack.
Games started outside top 6 --
Tigers -- 0
Oakland -- 5
Reds -- 6
Yankees -- 7
Rays -- 9
Braves -- 11
Guardians -- 14
Red Sox -- 18
Cardinals -- 21 -- If you include Carpenter who made 0 starts, they are at 30.
Pirates -- 25
Dodgers -- 26
Rangers -- 26
Blue Jays -- 27
Orioles -- 30
My point is that if your team has to rely on its #7/8 starters, and 2-3 significant arms get hurt, your team isn't going anywhere anyway.
I find it extremely hypocritical to say its a terrible idea to rely on pitching prospects as depth when you are suggesting relying on hitting prospects as starters.