Part of it just depends. For example, Allard is currently ranked at the back end of the top 100...but there's a decent chance he improves his stock over the next couple years. If he ends up in the top 10-20, then suddenly his chance of busting is nowhere near as high. And it seems to make sense that the guys who only ever reach the top 50-100 are either guys who are ranked high initially and then bust, slipping out of the rankings altogether or are guys who only reached the top 100 after climbing through the minors, at age 22-24 or so. And those are the guys like Folty who have pretty obvious flaws that keep them from climbing higher in those rankings.
So while it seems crazy initially that that many bust, it makes sense when you think about it.
I would advocate trading the guys like Folty when you get good value for them while keeping the guys like Allard.