Even if you got just 7 innings per start you'd have fresher arms for the post season, which should be your goal. have two long guys for bad starts, a lefty specialist, set up, and closer and you have 11 guys pitching.
One thing I'd love to see is them expand the ML roster to 28 players with only 25 being active for any one game. Your 2Bman needs a day off, okay, you still have a full bench. Yesterday's starter is no good to you now, no problem. Tomorrow's starter is out of the question because he's going tomorrow. I'd have it that no more than 2 pitchers can be on the inactive roster, but just a suggestion.
You are kinda right but teams can use the 40 man already for depth. Most teams use 5 of those slots to protect rule V.
But getting into a theory craft.
Cubs have (going off that Thor trade)
Lester, Hamels, Hendricks, Q, Darvish, Thor
2 x 5 inning arms. Chatwood and Montgomery
4 late inning arms: Morrow, Cishek, Edwards, Strop
12 pitchers. Then sign Britton or Miller. They could also use Edwards in the Thor trade and go after both Miller and Britton to really go for a high leverage pen.
All in theory of course.
I believe that the O was a mechanical issue myself. It should fix itself.