I have this theory: Most pitchers who have the ability to reach the major leagues have the potential to become good major league pitchers.
Consider this 21-year-old rookie: 6-14, 5.61 ERA, 155 2/3 IP, 181 H, 17 HR, 74 BB, 101 SO.
Would you have bought stock in those numbers? This kid was obviously young, so maybe he was rushed to the majors, but he got beat up pretty good. That kid was Greg Maddux, and the next year he won 18 games.
How about this 25-year-old left-hander: 6-10, 5.15 ERA, 153 2/3 IP, 184 H, 20 HR, 52 BB, 123 SO.