Unfortunately, as i stated earlier, good pitchers are pitching in starting rotations. Do you find some flaw with that logic?
"Pitching depth" is constituted by re-treads, guys not good enough to start on a consistent basis, and guys trying to come back from injury.
Again, a guy that's good enough to start on a consistent basis for a team (Joe Saunders) will sign a contract that allows him to start on a consistent basis for a team.