18yo pitchers today are MUCH more polished coming out of high school than they were even just six to ten years ago. A kid like Pint will have had top level training and pitching development through the best programs in the country for several years by the time they hit the draft. I think you can also think of pitchers a little different than position players. If an organization gets ahold of an 18yo throwing upper nineties, they actually have a lot of time to bring him along the way they want to. You might as well let position players develop in college and get their at bats in where there is little chance that they will injured or mismanaged.
Yes. They arme bigger, stronger and had Tommy John surgery.
Im not sure that it is good to push the developement earlier into the players age. Their muscles might be as big as a 20 year olds but the ligaments and bones are still developing. That puts a lot of stress not only to the ucl but also to the joints and cartilage.