I would definitely do it. It's hard enough for these prospects to pan out into viable big leaguers, it's even harder for them to become fantasy relevant in a 12 teamer. If you look at the waiver wire it's probably filled with some damn good MLB players who were once top 100 prospects as well.
McLain, Jones and Gavin Williams (unlikely to become an ace) are nice prospects but in order to make you regret it they've got to hit on the high end of their projections.
Cole is a stud and even if he takes a step back in the coming years (he's still only 32) he's still going to be a very good fantasy player.