You might be conflating launch angle (path of the struck ball) with bat swing angle (ie Zepp 'attack angle' or angle of the bat).
The 'perfect' launch angle is still 30 deg. As you point out, nobody typically swings with 30 deg bat angle to generate a 30 deg launch angle.
Balls struck at 30 deg launch angles are then obviously typically hit with 15-20 deg attack angle, and therefore is almost always in reality undercut with backspin. (This point is missing from everyone's analysis)
Almost everyone in MLB undercuts because the bat head drops below the pitch angle.
