Just a couple of points.
Obviously, there are more tall pitchers in the MLB than shorter pitchers. One question is, are there more because they are better or because MLB teams and scouts THINK they are better or will be better in the future, therefore, they are given more benefit of the doubt and more opportunities. The numbers would then be skewed because the numbers you are using are not only based on talent, but on some pre-conceived belief. I agree that MLB is about performance and that only the best get to the MLB. But if you look at the draft, it is also skewed towards the taller pitcher. So the pool of pitchers coming thru the MiLB starts off with a larger pool of taller pitchers. I'm sure all of us have heard the stories of MLB teams telling their scouts don't bring me anyone under 6'. I've heard it and I've heard others here mention it as well.
The more telling portion of the report above is the correlation of injuries to size. This has nothing to do with velocity, but purely about injury rates. I've heard it countless times that the bigger (taller) pitchers are more durable, therefore they are the guys teams want to pitch. This reports shows that the shorter pitchers are no more likely to be injured than the taller guys. So I think it debunks the myth that taller guys are more durable.
Whether there are more taller pitchers in the MLB because they are actually better or because they are perceived to be better or more durable, it doesn't change the fact there are more of them. But as others have said, what does it really mean? The chances of anyone making it to the MLB are miniscule. But kids have dreams. Kids want to pursue those dreams. Tall or short. The fact of the matter is, shorter pitchers with talent, determination and drive CAN make it there. Height is one thing that they cannot change, but if they work hard, there is nothing saying that they can't have the opportunity if everything else falls into place.
My son is a short RHP. I understand this reality and so does he. What I tell him is that if he wants it, he is going to have to be that much better than the taller guys and he needs to work hard to get there. I'm not going to tell him that he just needs to forget about it because he is too short. That would be very counterproductive.