Correct me if I'm wrong but it seems to me you keep drafting one until you find your QB and they haven't found him yet.
And even if you have one. Brady was drafted when Bledsoe was the unambiguous starter. Rodgers was drafted when Farve was the starter.
Watson is in his final year of his contract.
If they had used a second round pick it would be a different story, but he was the nineth guy they drafted. They may have drafted everyone they thought was worth drafting and grabbed the top guy on the UDFA call sheet.
If you cut a 6th round pick at the end of training camp he isn't a bust. He is just a guy who didn't work out.