in general, treat all those stats as window dressing. you need to be scouting players before signing them. that's the advice i'd give to anybody, at any level of experience or success.
on the more theoretical side of the conversation - i'm not convinced that there is zero correlation between those stats, and the ratings. sure seemed poor when i looked 15 years ago. i do sometimes wonder if those stats give more than 0 information though, like, is a guy with 25ppg on average no better in lp or per than a guy with 5 ppg? maybe. definitely the size of the high school or something seemed to be a factor. i wouldn't rule it out, that there *could* be a coach out there who is able to make a more educated than random guess, but still, a not-that-educated guess, based on those stats. its very possible there is absolutely nothing there, i just can't completely rule out that there might be something. and i doubt there's even a single coach in HD, who uses those in anything resembling a constructive fashion. i'm not convinced there COULDNT be, though.
but to the OP - this is a theoretical issue. nothing i just said changes that you really need to be scouting players and signing them off their ratings. also, we know for sure - if you know the ratings, the high school stats provide zero additional info. if you end up being one of the rare folks who goes and investigates corners of the game to find a rock to turn over, that even the best coaches in HD history haven't looked for - maybe then, you could go down this path. i seriously doubt that i would find anything useful, if i went down that path. and if i did, i expect it would be at best quasi-useful, and would have no real impact on anything. this is a corner that is a theoretical curiosity too remote even for me, and i tend to take interest in remote corners basically more than anyone. so like - ignore those stats - but maybe after you've mastered the game, if you want to look back, you *might* find something?