I think you need both. Guys like Aldon Smith and Greg Hardy are about as useless as EJ Manuel. Talent has the slight edge, because Smith and Hardy have contributed more to an NFL team than EJ, but they've also held teams back.
But I think we need to dissociate smoking weed with poor character. It isn't beating women, it isn't laziness, etc. It may be selfish or short-sighted because at this point they know they can lose their jobs for it, but they aren't worse people because they smoke.