Slight update! I've added a little overshoot to either end of the ball's climb, which softens things out and adds a little more realism to the whole thing. There's a weird kink at the very end caused by looping the video - I think the start and end positions don't quite match up or something. Need to figure out how to get the overshoot without it jerking like that!
I actually shunted the position of a couple of the keyframes around a little bit, mostly the second one. I moved it a little further to the left so that it hit the lowest point of the drop a little more quickly, solving the problem of it falling too slowly at the beginning.
I need to look at fixing the kink at the end now, as well as reducing the ball's hang in the air at the right side.