The whole complaining about ratings is ridiculous. There are tens of thousands of h.s. basketball players across the country. And a certain percentage are really good. I doubt the posters wondering why Epps is rated "only" 70 or whatever have seen the guys ranked above him. And if you're #70 in the country, that's pretty elite company.
The only player I've seen whose highlights leave my wondering why he's ranked "so low" is Dain Dianja. You watch his highlights and it's amazing the things he can do at 6'9 270. Yet out of H.S., I think he was ranked just barely inside the top 100. I suspect the answer is that you're seeing highlights. Which are very impressive, but may not show what he's doing the rest of the time. Which could be not playing defense or running the court.