I already wrote about this Pirates Prospects article here, but I think it's probably worthy of further discussion. The idea of the article is that the Pirates have a bunch of potential aces in their system, which I don't think anyone really disputes. What I do take issue with, at least to a degree, is the characterization of fastball velocity as the crucial component of acehood.
There’s an old saying that goes "In order to make bricks you need clay", which means that to produce something positive you first need the right raw materials. There’s more to a great pitcher than just a blazing fastball, as an ace will have 3 to 4 plus pitches in his arsenal. However, it is much harder to be an ace WITHOUT a great fastball. Of course there are exceptions to every rule — Cliff Lee is the current one right now — but the fastball sets everything up from that point.
To make bricks, you need clay - fine. But what if you could build the house just as effectively out of wood? There are lots of top starters who throw hard, it's true. But Cliff Lee isn't really an "exception." There's Dan Haren, Jered Weaver, James Shields, and a bunch of others who've had success without top velocity. The prototype of the "ace" does exist for a reason, but in practice, a whole lot of aces don't really look like that. Fastball velocity is a great thing, but many pitchers succeed without it, and many fail despite it.
In the cases of Gerrit Cole, Jameson Taillon and Luis Heredia, who all are well-rounded pitchers in addition to having good velocity, the distinction I'm trying to make doesn't matter all that much. In Stetson Allie's case, however, I think we may risk overstating his value as a prospect by focusing on fastball velocity. Sure, Allie is a potential ace. But the field of potential aces is, I think, larger than most fans believe, since many real-life aces don't fit the prototype. The actual chance that Allie will become an ace is quite slim, and if someone would like to argue that someone like Kyle McPherson (who has good, but not outstanding, velocity, and a much clearer idea how to pitch) actually had a better chance of becoming an ace, I'd be open to that argument.
Also, the Pirates' primary goal isn't to develop aces, obviously. It's to win baseball games. There are many ways to win baseball games, some of which involve the use of a frontline starter, and some that don't. Hypothetically, if McPherson has, say, a five-percent chance of becoming an ace and a 25-percent chance of becoming a good third starter, and Allie has a six-percent chance of becoming an ace and a 15-percent chance of becoming a good third starter or a good reliever, I'll take McPherson.
This is all very nit-picky. I suppose I'm just resistant to anything that sounds like hype, and the idea that Allie is a potential ace strikes me as mostly hype right now, even if it isn't false. (This isn't to say that you shouldn't buy Pirates Prospects' sure-to-be-excellent upcoming book, which features Cole, Taillon, Heredia and Allie as actual ace playing cards on its cover.) The concept of an "ace" is more complicated than most fans think it is, and even the concept of a "pitching prospect" is pretty darn complicated. When I see a bunch of guys in the same organization lined up in this way, I can't help but think of this.