What potential? Based on these threads it appears the Anti Heyward group hates him because he's not a 330 hitter that hits 35 HRs with a 980 OPS. Heyward has had a fine career and put up good numbers, yes it's been up and down but he had two serious injuries and is only 25.
He is a career 780 OPS guy through the age of 24
He has a career fWAR of 21.9 in 5 seasons and has been worth 151 million dollars in those 5 seasons
In what world hasn't he lived up to his potential?
Further, Miguel Cabrera accumulated a 22.2 WAR in his first 6 seasons. Are you going to try and say that Heyward was a comparable player over the same span?