I think the award goes to Perez right there, when you forget the guy exists
Lotsa guys come to mind for me, Jim Thome being a big one. I thought he would lead the majors in HRs, and well, while he was close, he didn't quite pull it off.
...Boston papers now and then suffer a sharp flurry of arithmetic on this score; indeed, for Williams to have distributed all his hits so they did nobody else any good would constitute a feat of placement unparalleled in the annals of selfishness. -Updike
To call Ollie an underachiever means he achieved something and I don't see how anyone could say he did that...he was just pure terrible.
Guys who didn't play bad, but didn't come close to expectations includes Beltran, Helton, Edmonds, Blalock, Renteria, L. Castillo, Berkman, Morneau, G. Anderson, and Aaron Rowand. Guys who don't have bad fantasy numbers, necessarily, but certainly didn't meet expectations.