Ok, maybe I'm overvaluing Pena, too.
Pena's Top 10 most similar batters through age 23.
A LOT of big time sluggers on that list: Barfield, Colavito, Bobby Bonds, Horton, Killebrew, and Maris. If Wily Mo has a career like ANY of them, he will be -a lot- more valuable than Bronson Arroyo.
The other guys in Pena's list include Kingman, Incaviglia, Montanez, and Billy Conigliaro. Kingman's not bad, while the other three weren't that great.
Averaging those ten guys and adding their age 24-end of career numbers to Wily Mo's results in the following projected career line for Wily Mo: .259/.334/.470, 301 HR, 117 OPS+. Not a superstar, but not bad at all.
PECOTA mostly agrees with baseball-reference.com, pegging Barfield, Willie Stargell, and Incaviglia as Pena's top 3 comparables.
Bronson Arroyo's top comparables list
includes names like Mike Harkey, Kevin Foster, Chad Ogea, Scott Sanders, Ted Lilly, Sean Bergman, and Brett Tomko.
PECOTA's top 3 comparables for Arroyo are Dick Ruthven, Esteban Loaiza, and Danny Darwin. Better than the guys above, but still mediocre: only Darwin had a career ERA+ better than 100.
To me, it's pretty obvious that Pena has a much better shot of being a valuable commodity in the future. Or am I also overrating him?