One HS pitcher didn't work out (Stetson Allie) and that's your justification for not taking him? Give me a break.
How many corner college outfields, who hit for little to no power and don't have elite speed, have ever worked out well in the majors? And how many of them would have been worth a top 15 pick?
Difference makers on the mound are what separates the haves from the have nots in MLB. Teams that win titles have top of the rotation starter....a guy who can kill losing streaks and flip momentum. Teams that don't continue to select in the middle of the 1st round and take guys like Naquin with their 1st round picks. He'll be good enough to likely make an MLB club some day but won't be an impact player (unless he busts through a massively high ceiling that few think he has).
Giolito has a + fastball and a + to above average curve at only 18 years old. Those guys don't grow on trees, especially ones with his physical stature. At 6'6", 235 LBS you can certainly dial back some of that velocity and comfortably settle him in around 94-96. He has a great stride and should easily be able to relieve some of the pressure on his arm through lower body training.
We're talking about a guy who was a lock to be a top 5 pick pre injury and could have even gone #1 overall had he worked out well. Surely you take in to consideration him tweaking his elbow but at #15 in the draft you select him and run to the bank. He has the potential to have #1 starter stuff and instead of rolling the dice on him you take a college outfielder half a round early who has no pop in his bat. I guess I just don't understand the logic but hey, what do I know.