I really don't agree that Rizzo's season is as bad as some has suggested. But let's start with Cashner. He's 27 which is generally considered to be the start of your prime. He has a 3.40 ERA and 3.77 xFIP. He pitches in a pitchers park where his ERA is 2.14. On the road his ERA is 4.41. His 6.45 K/9 is 66th out of 83 pitchers with qualified innings His BB/9 of 2.66 is 39th out of 83 pitchers. In my opinion, he appears to be a back of the rotation starter at best. Travis Wood and Cashner have roughly equivalent numbers.
As for Rizzo, I've already detailed my thoughts on him in numerous topics. But simply stated, he's 24. He's well before most players prime years. His metrics suggest he's been unlucky to some extent. His OBP suggests that if he figures the issues out that are causing him to pop up more pitches that he will be better than his numbers the previous year. But even then, his major stats aren't that bad. And there's significant reason to believe at age 24 that by age 27 he will be better. Cashner getting substantially better at 27 is far less likely.
Now, it's worth noting, that 1B is a position where your better hitters reside. And if Rizzo doesn't develop into an elite hitter, he might hold the team back. But, we're not at that point yet and even if we do get to that point, Rizzo has already proven he is as good as solid major league players like Adam LaRoche. It's also worth noting that pitching hasn't been the cubs problem. In the future, they are missing a top of the rotation starter in their farm system but I think it's a huge stretch to suggest Cashner is going to be that type of player. This is by far the best year he's had and we're talking about a 4-5 starter numbers.
So, my answer is I'm glad they made the trade and I'm willing to bet Rizzo far out weighs Cashner's WAR and that's before considering things like Cashner's injury history and the fact he's much closer to being a FA than Rizzo.
