There is no reason to believe this, Sheets has been better over the past 4 seasons (albeit with an injury) and he's been better this year. At best its a push, at worse its advantage Sheets. Ok, now I hate position-by-position comparisons as much as the next guy, since they are truly a meaningless "metric" of team comparison, but there is no way Sheets has been better than Zambrano over the past 4 seasons. This year, absolutely. 2003-2006, Zambrano has had a higher ERA+, better ERA, higher VORP, and more Win Shares each year. Sheets beats him in walk rate easy, but that's about it.