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What's weird about the letter (http://www.ussmariner.com/2007/06/27/an-open-letter-to-rafael-chaves/) is that Cameron's principle complaint wasn't that that Felix threw too many fastballs, it was that he started off the game throwing too many fastballs. You know what, in his perfecto he threw seven pitches in the first inning - six fastballs. In the second he threw ten pitches, seven fastballs. Not much has changed in his pitch selection. What has changed is his control of the fastball and the quality of his off-speed stuff, which right now is probably the best in baseball.
Barring injury, there is no reason he couldn't throw just like this for another dozen years.