It's easy to defend Cassel with stats.
"In years he wasn't saddled with a horrible supporting cast, or had his team suffer injuries, he has a magnificent 48 to 18 TD/INT ratio!"
Alex Smith's current 9.8 YPC is one of the lowest marks in the NFL over the last 10 seasons. Only a few QBs have been worse:
Ryan Mallett (9.8), Derek Carr (9.4), Christian Ponder (9.8), Brady Quinn (9.8), Ryan Fitzpatrick (8.6), Brodie Croyle (9.7), Charlie Frye (9.7), Bruce Gradkowski (9.4), David Carr (9.2)