To throw 100 you need both talent and hard work. There are a few guys who can throw 90 plus with just playing catch and a few push ups but those guys are very rare, most guys have to train extremely hard.
Usain bolt is super talented but he trains at least 5 hours every day. He wouldn't wun that fast if he did 5 sprints twice a week. But likewise I wouldn't run as fast if he did his training regimen.
Pitchers are athletes and athletes are both very talented and they work very hard. Harper and greene are both exceptional talents that worked very hard since they were 10.