First, the best talent evaluators in the world might not get Myles Garrett. I would venture a guess that Stoops was well aware of Garrett's talent. That we didn't get him hardly means that we didn't properly evaluate him. When you coach at for the UK football team, you don't always get the talented players that you would like to have. But it doesn't mean that you couldn't evaluate them.
Second, the first full class from this regime was the 2014 class. We'll probably have three players drafted from that class- Edwards, Ware, and Baker. We may get lucky with another player or two- perhaps West, if he gets healthy. Perhaps Juice. Middleton might have a shot. It gets even better for the '15 class- Conrad, Westry, Baity, Allen, Jones, Stenberg are all legitimate prospects, and we may have others. 2016 and 2017 might even be better, though it's too early to speculate for most of these guys.
Finally, the NFL draft does not entirely translate to talent evaluation at the college level. Boom Williams was an excellent college running back- SEC caliber all the way. His particular skill set didn't translate to what the NFL is looking for, though he still may surprise a free agent. It doesn't mean that he wasn't properly evaluated, and offered, as a SEC impact player. Stephen Johnson is highly unlikely to hear his name called next year. It doesn't mean that he is not capable of leading us to another bowl game. There have been undrafted Heisman winners. But their college coaches still managed to properly evaluate their ability for the college game.