Talent refers to physical ability, not accomplishments. I have never seen nor heard of a 17-year old with his physical talent and size. He is better than both Strasburg and Verlander were at the same age. Comparing him to other top HS pitchers isn't appropriate. It's like comparing Bryce Harper to other top players his age from previous drafts. Giolito is a freak, much like Harper (Not on that level, but close). Those don't come along very often.
This doesn't mean he will be a star, or even make the majors but anytime you have a chance to draft someone with historic talent (as in no one has ever had his gifts at his age) you do what you can to sign him. He may be a bust, but he has the gifts from God to be the best ever at his position. You don't let guys like that get away if you can help it.
best pitching prospect slipped out of the top ten because he may need surge try with a 90% success rate? Tons of pitchers were better than Stras and Verlander when they were Giolato's age- they aren't anymore, that why high school pitchers are such a crap shoot