Ideal "launch angle" for hitting home runs

In theory an object travels the longest horizontal distance when it is launched at a 45 degree angle.  But very few home runs come off the bat at a 45 degree angle (most such launches would result in a "pop-up."

There are multiple contributing factors (several discussed here), but the simplest to understand was provided in an ELI5 post:

It’s mainly because the air resistance increases in proportion to the square of the velocity. So if something is going twice as fast, it has 4x the air resistance.

The ball leaves the bat going very fast (up to 121 mph), so at the beginning of its flight it slows down quickly because the air resistance is much higher. If we want the ball to go far, it needs to cover more horizontal distance while it’s going fast, so it’s better for it to be moving at an angle shallower than 45 degrees during that time. If it leaves at a 45 degree angle, the horizontal velocity is lost more quickly (edit: more quickly in terms of how far the ball has moved horizontally over a period of time)

Addendum:  FWIW, I would have some doubts about the regression line in the graph.  I'm surprised the r^2 is that small given the scatter, but perhaps some dots represent multiple events. Anyway, the explanation is still valid.