I know it is not new, I just think it is ridiculous.
Several years ago, Bill James wrote something along the lines that he didn't care for the term "overrated" because, without understand what "rating" you're talking about, it doesn't really describe anything.
Maybe Stark defines what he means by "overrated" in the book. I don't know, because I haven't read it.
I think the argument about Ryan is that he was not as effective a pitcher as, say, Seaver, but you hear a lot more talk about Ryan than you do about Seaver. Ryan wasn't as good as Seaver at keeping runs off the scoreboard or winning games.
But I don't think that's entirely what people think about when they think of Ryan. With apologies to Sandy Koufax and Randy Johnson, he was the most prolific power pitcher in history, which is why his strikeouts and no-hitters are off the charts. In this way, Ryan was perhaps more unique than just about any other pitcher in history. That uniqueness is what creates the aura around him.
So, if "overrated" is defined to mean pitchers that are revered above where they rank all time in ERA and winning percentage, then I suppose Ryan is overrated. But that seems like a pretty limited definition.