That's just not true. For much of the season he was playing outside corner with Woodson in the slot. Our CBs moved around a lot. When Woodson played slot, are you going to say he wasn't challenged because he wasn't playing man coverage on the team's #1 WR? I'm not saying Shields is perfect, but you're not giving him credit for the things he did.
He played outside, meaning he covered ones and twos, quite often.
And being a primarily zone team, none of our guys are on an island. They perform as a unit. They either succeed as a unit or fail as a unit. And much like the offensive line, our secondary is truly only as strong as the weakest link. Perhaps Shields was the weakest link. If this is what happens with Shields as the weak link, I'll take it.