You cannot catagorize what a "5.0" player can do. Some have guts, determination, and make the best of a poor athlete's skills. Other's can hit 7.0 shots occasionally, run as fast as 7.0's, but haven't been playing long enough, didn't get the coaching, or ON THE WAY UP ! On the way up means they have the skills to make 7.0, but aren't experienced YET!
What you say generalizes a 5.0 as having limited shots, limited potential, and that they can get only as far as they already have. You are limiting them by catagorizing their "age" and experieince, without knowing WHO they are.
And some juniors grow really early, peaking their heights at 14. Other's are STILL GROWING at 20, and their athletic peak is much later than the former.
Catagorizing is what general USTA teaching preaches. That's why we have NO future in the ATP tour with our current juniors.