Hitting is what HS coaches seem to care about most, so if there is a better hitter in his primary position, he will not play it. This to me is a shame as I find far more games lost to poor defense in the core up the middle positions than lack of offense. so if he wants to play make sure he hits well and can play multiple positions, honestly he won't need to be able to play them super well (just field a grounder and track a fly). As far as core position focus, I think that really only applies to those positions you are 1. pigeon holed into (first base - so many nuances to this position that aren't taught and demand better players) or 2. those that demand specific skills and knowledge (Catcher,Pitcher) - but still need a backup position.
Third, right and left are your fill in positions, everything else demands top defensive ability. I know a bad team and poor coaching when I see 6 guys listed as 1st baseman/DH's and 3 more at 3rd/DH.