The ship has sailed, but he was definitely good enough to play and he was definitely blackballed. Even if he's not a good starting QB, he was better than at least 2/3 of the guys on the bench. This is not debatable. He took his team to a SB. He was still fairly young. His stats in his final season were pretty solid, his team just really, really sucked. I mean, he was clearly better than the Blaine Gabbert on that same roster in the same situation, and BG is still in the NFL, just cashing checks as a truly terrible backup.
You see Mason Rudolph on an NFL roster as a 2nd stringer and really think that Kapernick wasn't good enough to be in the league? If you think that then you don't watch enough NFL.