Depending on the kid, the intent to hit line drives, if missed slightly, can be a hard hit ground ball as opposed to a fly ball.
Fly Balls are outs in HS Varsity. Ground Balls are usually outs but not always.
The "Me First" attitude and not listening to "some dumb coach" in High School is the biggest concern, but that is more of a generational thing from the current generation of kids and current generation of Boomer and Gen X parents. Kids learn the wrong things and suffer greatly at the next level (if they even can get that far!) with lessons that are more painful and eye opening, if that is the lesson they are taught at home.
I agree with learning launch angle, I agree with knowing where it hits in the cage can tell you something about hits vs outs.
Not sure a "grooved swing" should be the goal, but perhaps that is semantics. Bases loaded, late inning, 2 strikes, and you are trying to elevate a slider on the outside corner of the strike zone? I've seen a lot of kids look lost with 2 strikes in general as it is, because Dad/Coach has hammered into them a "elevate like Kris Bryant, don't listen to your coach kid" attitude. No ability to adjust, no ability to expand the strike zone, no ability to just get the ball in play and move a runner over & help the team.
A vast majority of kids like that, if they are fortunate enough to even get to college ball, have to relearn how to hit in college or get labelled PO's before they ever get a chance.