This might just be me, but I don't think any MLB player consciously goes through a swing trying to produce a 30 degree launch angle on a pitch. It seems more of a by product of a bat angle, or how much you swing up at the baseball. The thing that seems to be controllable is bat angle and depending on how good your hand eye coordination is, will come out a certain launch angle. I don't necessarily think Cozart has pefect hand eye coordination because his bat angle seems to line up with launch angle (-8 to -15 BA, compared to a 13 LA), compared to maybe a Donaldson, with a 35 LA with the same -8 to -15 BA. This probably has to do more with mentality in knowing how much power you have and where to aim to hit the baseball. A common thing throughout all levels of baseball is knowing what type of hitter you are, as Jean segura (leading the MLB in average) is probably going to aim higher on the baseball than a Donaldson. I would argue that almost every player in the pros swing at an upward plane for best results with maybe the exception of Mookie Betts.