First, while Jake is older than Darvish, it's only by a few months. And Darvish has thrown over 400 more innings than Jake has. That's the equivalent of two full seasons! If the question is which is farther downhill in his career, contrary to what most Cub fans seem to think, the answer is clearly Darvish. Moreover, even though he has more miles on him, Darvish has never achieved what Jake has. And he never will. Darvish has never won the Cy Young award. And on top of it all, Darvish has had Tommy John surgery. Jake has not. Darvish is damaged goods.
But the proof of the pudding is whether you can rely on a guy when the chips are down. Jake Arrieta's post-season ERA is 3.08. Darvish's is just south of six. Arrieta not only won two World Series games to Darvish's none, but he's 3-0 in elimination games. He's never lost one. In those games, Jake's ERA is 1.27.
Ok. You're the manager. It's Game 7 of the World Series- or any other game you absolutely have to win. You can start either Arrieta or Darvish. Don't tell me that you're going to pick Darvish unless it's 1919 and you're the White Sox.
In short, Darvish is damaged goods with more miles on him, and a track record of failure when the chips are down. He has never accomplished what Jake has, and is actually farther downhill in his career than Jake is. There is basically no significant difference in age, but Darvish's arm is not only surgically reconstructed but has the equivalent of two more seasons' wear and tear on it.
Jake is a former Cy Young Award winner with a track record of being stellar in the post-season and who has not only never lost an elimination game but has been consistently lights-out in them. Granted, he's not the Arrieta of a couple years ago. But Darvish isn't even the Arrieta of today.
And the critical point that when the chips are down, he isn't even close to being the Arrieta of today. Folks, I don't think it's a difficult choice, and if the Cubs end up signing Darvish when they could have re-signed Arrieta for essentially the same money, the evidence suggests that they're going to regret it. And I am going to be both very disappointed and very pessimistic about their chances even if they manage to get to the Series, which I don't think they will if Darvish is in the post-season rotation.