If you actually watched Nogueira fight throughout his career, you'd know he was pretty much a shot fighter by the time he fought Sylvia in Feb '08. He'd been on a gradual decline since about 2004, but it was only by '07/'08 that his performances hit a low and never ever recovered. The difference between Nogueira of 2001-2004 and Nogueira of 2007 onwards is very clear.
As I said earlier, Nogueira is the Roy Jones of MMA. Roy Jones gave us the warning shot of the 1st Tarver fight that he was seriously on the slide, and then after the rematch loss, his career never recovered. The old Roy was gone. Similar situation with Nog. He didn't look right in the Herring fight in the UFC, then performed poorly vs the inferior Sylvia, and then never ever looked like himself again.
Pre-Sylvia, Nog beat:
Crocop, Barnett, Werdum, Kharitonov, Rodriguez
Post-Sylvia, Nog beat:
Dave Herman, Schaub, ancient Randy
I mean, come on. The guy got old. I don't rank Roy Jones below B-Hop just because Roy fought on too long and got smashed by guys he would've embarrassed in his prime, and I apply the same standards to Nog and the rest of the MMA world. If Jon Jones fights on till he is 40 and starts to get beat up by C-level fighters in his later years, it's never going to change how good he was in his prime or what he did at his peak, and that's what really matters.