There are so many reasons -- besides trying to win the World Series this year -- to upgrade any starting rotation with established MLB winners, ERAers, WHIPers and FIPers:
1. Inning eaters who take a regular turn give the rest of the staff a break; bullpens are less taxed, and better able to relieve the starts of other rotation members, free to be themselves and pitch with impunity, knowing fresh arms are ready in reserve behind them.
2. Not only can reason #1 prevent physical and mental injuries on the roster this year, such health can carry over into subsequent seasons... and thus expedite the "timing" for contention.
3. Reason #1 can also take the pressure off an ace's defense and offense, and lead to Reason #2...
4. ... because virtually every retired player who is now manager, coach or media voice continually extols the value of having veteran leadership in the clubhouse, dugout and bullpen -- someone who can not only teach younger teammates, but also show how it's done on the field (something Cora, Breslow and Bailey can no longer do).
5. Prices for quality starting pitchers are always going to increase -- and you've got to start somewhere.