Kyle Gibson - Gibson heads this list less because he has been overrated, I think he is a top ten prospect, than because of the expectation that he will help the Twins this year. Its possible, but not very likely. There are at least six pitchers ahead of him for spots in the rotation. Unless performance or injuries create a couple openings, it won't matter how well Gibson does at AAA. Gibson has only faced 621 professional hitters, only 64 at AAA. Even if the Twins have an opening, Gibson is probably not the first choice based on that limited experience. Scott Baker made a similar fast rise through the system in 2004. Gibson was more dominant than Baker, but Baker faced 241 batters in A ball. It was a couple more years before he was really ready to help at the major league level. And the Twins are unlikely to add Gibson to the roster unless they are convinced he is ready to help immediately.
Joe Benson - Benson has good defensive skills. But on offense he has been an all or nothing hitter. The "all" part of that has impressed a lot of people. But the size of the "nothing" against AA pitching is disturbing. It is only likely to increase as he faces tougher competition. He looks like a fourth outfielder if his defense is as good as advertised. That one dimensional bat will keep him from playing every day. If his defense doesn't play in center field, he is a career minor league player with impressive power numbers.
Oswaldo Arcia - Arcia is one of a long line of players who have had "breakout" seasons at Elizabethton. None of those players lived up to the hype their numbers in the Appalachian League created. The problem is that Appy League players are mostly very young. A player who matures ahead of his peers will be very impressive. But as the other young players mature, that lead disappears. At 19, Arcia is younger than most of those past one-season wonders, but it would still be a good idea to check the enthusiasm until he does something at a higher level.
Liam Hendricks - Hendricks is another player who had a "breakout" last year. He put up impressive numbers at both Beloit, in his second season, and at high-a ball Fort Myers. Hendricks is a guy who throws a 90 mph fastball. His strikeouts are based on outstanding control. He is fooling A ball hitters. Whether he can fool more experienced hitters remains to be seen. In addition, Fort Myers is known as a pitchers park in a pitchers league, especially during the hot, humid summer months when Hendricks was pitching there. This is another case of wanting to see him do it again, rather than anointing him a top prospect based on one limited season of success at a low level.
David Bromberg - I hesitate a bit to put him on this list for two reasons. He doesn't have the over-enthusiastic projections of the other four. And he has consistently made his detractors look bad as he moved through the system. Nonetheless, he doesn't look like a major league starting pitcher. Not even at the end of the rotation. And he doesn't look like he has the stuff to be a major league setup guy. That means his upside is as middle-reliever who fills out the bullpen. That may make a career for him somewhere, but probably not in an important role on any really good teams.
To be clear, since most prospects fail, you are likely to be right at least half the time if you just randomly identify five players and say they are overrated. In other words, it is easier to be right picking losers than picking the winners. So at least three of four of these evaluations need to turn out to be true to say more than "most prospects fail".
All five of these players are real prospects with a chance to contribute at the major league level. They are all highly rated by someone, in the top ten or close to it. But I think the most enthusiastic projections for them are over-enthusiastic. For instance I will not be totally shocked to see Hendricks or Arcia in the big leagues, but I will be very surprised to see both of them. And I will be not be surprised if neither one is even on any prospect lists 3 years from now.