Like I said, size is not the end all be all for throwing hard. Mechanics are, in my opinion, even more important for throwing hard. That being said, even the short guys tend to have a solid build. 5'9" 190 and 5'11" 220 are both very solid builds. Just like with the Tim Collins example that I posted in the article, they wouldnt be throwing that hard if they lost 40lbs of muscle. Tim went from 5'5" 131lbs to 172lbs over several years and bumped his fastball up from 83 to 97mph.
My point is that rail-thin pitchers rarely throw hard, at ANY height unless they are extraordinarily tall. There are exceptions, as I keep saying.
This isn't a conversation about scouts or opportunity, but simply velocity. How much force a pitcher can transfer efficiently into the ball.
The kid who is 6 feet, 140lbs may very well be able to succeed as a pitcher, even throw reasonably hard. But in most cases, he will not have maxed out his body to the point where it is no longer the limiting factor in his delivery.
Maybe after he hits 180lbs, he stops improving his velocity...getting him to 210 may not be as big of a priority because now his mechanics...or something else is the limiting factor.
"So if you have a 5’9” kid throwing 90mph do you tell him to give up because he’ll never reach the size of ML pitchers?"
I stated in the original post that pitchers of any height can make it, and should use the weight ranges of MLB pitchers THEIR height as a general guideline of what to shoot for. It's obviously a generalization, but 170-190lbs is a low estimate for what most hard throwing pitchers that height weigh.
So if my 5'9" 90 mph pitcher weighed 150lbs, I would absolutely have him working hard to reach 170lbs, which is by no means "bulky." If he made great gains and was suddenly throwing 92 or 93, then keep getting stronger until those gains stop coming. Maybe he maxes his body out around 175 or 185lbs. Suddenly he has bigger fish to fry, mechanically or mentally to get him to the next level.
As for people getting less flexible or mobile from lifting, that is another issue entirely, and crappy strength coaches, programs or improper form are to blame. A balanced program where the athlete uses full range of motion and does soft tissue and mobility work will actually improve flexibility, not hinder it.