He got overrated because nobody ever used to throw at him so he never gave up many completions. On the raiders he only ever played man coverage on the defensive right side of the field (the lesser used side of the field by most right-handed QBs). The raiders sucked vs the run so they didn't get passed against that much to begin with and if teams wanted to pass they just put their best WR on the side away from him. He was still good at man coverage but he was god awful at tackling. Overall was a good player but comparisons to Revis and the contract Al Davis/The Eagles paid him were just ridiculous.
I think once he got paid by the eagles and they took him out of his comfort zone and play some zone and on diff parts of the field he just checked out.