A saying that still gets used is TINSTAAPP, there is no such thing as a pitching prospect. Obviously, this is an exaggeration, but there is a lot of evidence that lets people know how unwise it is to fall in love with pitching prospects. They blow out their elbows, they never develop a third pitch, their velocity declines mysteriously. There are a ton of things that can go wrong.
Still, pitchers are brought along at nearly the same pace as position players. They are vastly different entities, yet they are widely treated the same. Pitchers' velocities tend to peak early on, many peak before they ever make it to the major leagues, so their hardest pitches are wasted on amateurs and minor leaguers. That is why it is imperative for teams to bring up their pitchers more quickly in order to give themselves an advantage over other teams.
Now do minor league pitchers get better with the instruction they receive there? No doubt about it, but the best coaches are at the highest levels (whether that totally makes sense is a debate for another day), so pushing them quickly will lead to the best possible instruction to maximize their abilities.
You have guys like Mark Prior and Stephen Strasburg who are ready to go straight to the major leagues from the draft. After dominating college to that extent, there is no justification for keeping a guy in the minor leagues just because that's what you do, and these guys were ones who were brought up to the majors incredibly quickly, but even that was a waste. There was no better Strasburg than the one that the Nationals signed. He was as good as he would ever be, but they wasted starts in the minor leagues. Most college first rounders are probably ready to pitch in the major leagues immediately. Could they refine some things? Yes, but their stuff is going to be taking steps back as the years go on, and not everybody gets that much better with command and mental aspects of the game to make up for that. Neither guy had to wait long, but they shouldn't have had to wait at all.
Jose Fernandez is a great example of what I'm proposing. He was brought up after one full year in the minor leagues where he never pitched above High-A. People thought they were crazy for bringing him up so quickly, and all he did was dominate the league to the tune of a 2.19 ERA. There are other guys that are plenty ready to play in the major leagues, not to that extent, but an ERA in the mid 3's could really help out teams that are struggling through their fifth starters.
The whole point of waiting to bring up prospects is to get their best years performing for your team. With position players, delaying their major league debut makes sense as they go through a lot of growing pains and tend to get better as they get deeper into their 20s before declining. With pitchers, it's different. Their raw physical abilities are peaking in their early 20s, so promoting those guys so they are using that stuff against the best competition would give teams a huge advantage. Replacing a fifth starter with a top prospect could add 2-3 wins and be the difference between slipping into the playoffs and winning a World Series or hanging out at home and wondering what could have been. Will they get injured if pushed to the major leagues? Yes, probably, but just about every pitcher gets hurt these days, and the increased danger to arms is negligible compared to the benefits a team could gain from this strategy.
There Is No Such Thing As A Pitching Prospect. It sounds ridiculous, but with an aggressive promotion plan for top level pitchers, TINSTAAPP could become a wonderful reality.