Simple. It's a measure of how far a fall from grace a player can make, and how shaky the foundation of his perceived greatness was to begin with.
He played here for 10 years and for almost the entire time, how good he was was debated in a way other 'great' qbs aren't. Elway's greatness was never debated by Broncos fans. Nor was Rodgers, Paytons, Brees's, Brady's, Warner's, Roethlisberger... even guys like Luck, Eli... who they were and what they contributed to their teams winning was fairly universally known. With Russ, his STATS forced a debate that questioned his place among the greats because the numbers said so. But his play in a traditional (fundamental), sustainable sense... not so much. And so now, to a degree, sans the LOB to lean on. Sans top 10 running games to support him, sand Pete Carroll to 'hold him back', it's a bit of a truthing period, where absent the elements who made him or broke him, he can just show who he is as a qb, without the very specific stage he was provided to do his deal in Seattle.
It's interesting because now the question can be answered as to whether Russ could have ever been 'Russ' outside of the Pete Carroll Seahawks. So far, the answer is no.
I don't know how one can't care to better understand what it was they were seeing over the 10 years Pete and Russ were here together, given how hot the debate raged the entire time.