I complain about Stubbs regularly just as I complained about Knapp before him. After the Phillies finally cut bait on Knapp - another mediocre defense, poor offense catcher just like Stubbs - he was not able to stay in the majors with another team, which I think proves the point. I'd bet Stubbs would find a similar fate. If a team wants to contend for a World Series, it cannot ignore any position and waste roster spots.
A backup catcher should either be superior offensively or defensively, not neither.