Bum is correct. There is a misconception about guys that throw hard especially younger players. There are alot of younger players who have average to below average velo that can not command.
At a pro style tryout or workout etc you are looking for the players that stand out above all the rest. You look for seperation in ability. Once you have done that you look for the factors that will seperate those players. Ability to actually play up to your tools in a game situation. Ability to command , actually pitch , actually hit in game situations , ability to actually use that speed in a game situation , ability to actually defend , make up etc etc.
And this can change in a short period of time at these ages. I remember a kid named Levi Micheal who came to one of our tryouts and we sent him on his way. He just didnt do anything to seperate himself from the other players. Another was Shawn Armstrong a Rhp who have very average velo and was very awkward in his delivery. One year later Micheal shows up at a tryout and is the best player there. He was a freshman AA at UNC last year after passing on his sr year in HS. Armstrong would blossom into a low to mid 90's rhp in just two years and would drafted and ended up at ECU.
So things change and some things dont change. But believe me when your looking at 100 kids in four hours you have to look for the tools that seperate players. Then you look for the factors that seperate those players. You miss on some kids because at the time their tools do not stand out. You miss some kids because some play way above their tools. Eventually the cream will rise to the top. And that cream will be just fine.
But if your attending a workout / pro style tryout and your tools are averge , your tools will not allow you to stand out above the other players present , you will not be selected. That doesnt mean you will not get benefit from the event. It gives the player an idea of where they stack up. If gives them esperience they can draw upon in the future. And it lights a fire under the a** of the guys that want to be the best.