I think you're 1/2 right: starting pitching is more important than the pen in the regular season. Innings do indeed need to be eaten. My dad's favorite pitcher was Wilbur Wood, the White Sox knuckler, who often started both sides of a doubleheader. His best single season innings total was 376. Today, you'd be happy to get that single season innings total from 2 starters!
But come the playoffs, it's the exact opposite IMO. Think of those awesome Tigers rotations...Verlander, Scherzer, Price...and then they handed the ball over to that year's version of Byung Hyun Kim
Caveat: Unless you have a few Bumgarners.
