My opinion is the post season needs to test your entire team depth, and right now it does not.
MLB has decided they want the star pitchers pitching, the end. They have designed their playoffs with enough days off to ensure teams only need 3 quality starters for the playoffs. They only need 4-5 RPs assuming they get the expected production from each starter. You could limit a playoff roster to 18 guys and we'd see very little difference from the current post season.