Ben Sheets and Roy Oswalt both came up in 2001. Oswalt is 112-54 while Sheets is 73-74. By some statistical analysis it could be said that Sheets is the equal of Oswalt. But the object isn't winning statistical battles it's winning. Therefore Oswalt has been considerably more valuable to the Astros than Sheets has been to the Brewers. The job of the starting pitcher is to hold the opponent to fewer runs than his team scores while he is on the mound whether that means 6 runs, 4 runs, 3 runs, 2 runs, 1 run or 0 runs. Most of those pitchers considered all time greats did this consistently. Now over the course of any particular season, factors such as run support, bullpen effectiveness (more so in the past 30 years) and luck play a part one way or another but over a career these tend to even out to some degree. When your teams "ace" only wins 12 games it puts quite a burden on the rest of the team to get the 78 or so more wins needed to get to the 90 usually needed to get to the postseason.