Personally, I don't think Kam is even close to being the most over-rated Seahawk. He was not up to his standards last year, but that had little if anything to do with his ability and everything to do with his holdout (which vastly affected his conditioning) and the headaches that came with having a new DC who was trying things out.
The most over-rated Seahawk is probably a supporting cast guy, someone like Luke Willson, Jordan Hill, Cassius Marsh, Brock Coyle, etc, etc, etc. Guys that are all replacement level contributors, but get treated like up and coming players on local sports radio. Kam, when right, is one of the biggest difference making safeties in the game.
But I don't think Prisco knows the Seahawks well enough to name the lower tier players, or is aware of their reputations. Or maybe he does, but wants a name that national audiences will recognize. Among Seattle's flagship players, truly none of them are over-rated or on bad contracts, which is a big reason why Seattle is such a dominant team. So I think he picked Kam because, in 2015 alone, Kam came the closest to being over-rated out of Seattle's flagship group.
However, the fact that he named Kam the most over-rated in the NFL reeks of sour grapes. Prisco seems to live in a bubble at CBS where his co-workers are afraid of him and his assertions are not properly challenged. That has enabled him to take some fairly ridiculous, homerific positions on things and not think twice about it.