I agree with young people being stronger than we give them credit for in terms of their preparation for failure.  If you address the pitfalls to the young person, you can prepare him to handle those failures a lot better than if you hadn't.  Either way, they can learn from those failures and either Get Better or Never Learn.  Those are their two options everyday of their professional careers.  Ask Torii Hunter.  He's played for 19 years and still knows how to learn from mistakes.  You can only ruin a kid if you don't prepare him mentally.  The physical tools will / should take care of themselves (if they have any). IMO

That being said:  Every prospect in the Twins organizations AA needs more work.  They are not better than the guys who are already up their right now (MLB).  So why give up on a season before it has even begun.  Buxton, Sano & Walker lead the League in K's.  Only a small sample size, but does show they have some work to do in the coming weeks before promotions are thought about.  Might not be long from now, but definite work to be done.

Buxton, Sano & Walker are now seeing a better quality of breaking balls.  It's early, but if they don't turn it around in AA, none of them will make it to MLB.