Dylan Bundy might be the best pitching prospect in all of baseball.
Karsten Whitson and Dylan Covery didn't sign in 2010 and the next highest drafted HS arm (Mike Foltynewicz) is 10-2 with a 2.59 ERA this year.
Hobgood has been ruined by injuries but Zack Wheeler (taken one pick after him in '09) looks promising.
Ethan Martin is still a good prospect and Gerrite Cole was the 2nd HS arm taken in '08.
Jarrod Parker & Bumgarner were the first two HS arms in '07.
And like you mentioned, Kershaw was in '06.
How is that an overwhelming majority of busts?
Regardless, none of those prospects were considered as good as Giolito (pre-arm injury) coming out of HS.
I missed Parker going through the list- that changes it to a little under 1/2 success rate (Parker Kershaw Floyd)- I think you have to cut it off at 08/09- some guys (Bundy) look good, but until they play in the majors I don't think you can call them successes