I have come around to the idea a few things are really important to be recognized as a potential D1/JUCO/Strong D2 hitter, since travel ball pitching and most HS is so watered down.
1. Weight / Strength - 5'10" player that does not play a speed position needs to be 190 - 200 and the taller the heavier. Must be really strong and flexible.
2. Swing mechanics must be pure like a swing on the PGA Tour. Everybody swings differently, but the best reach the same points in the swing. The mannerisms and approach might be different, but there are certain things all good hitters or do well. I think good mechanics generate better contact/ball flight and consistency
3. Since travel ball is watered down, be effective against facing a hitting coach or good pitcher that can throw multiple pitches with movement or off speed in a cage or practice area.
I don't know any other way a good hitter can be evaluated if they are not playing in some sort of area code games or PG National type event. Maybe high school districts / playoff games. I am no expert, but and don't have all the answers, just a couple ideas.