QBs have an opportunity on every offensive play to be the difference. It is probably the only position that should be judged by playoff success.
The fact that he only went to the conference championship once is a bigger indictment. I could understand if his teams weren't good enough to win the Superbowl, but to not get them to the conference championship more than once is not great. Especially when he had teammates like Tomlinson, Gates, Gordon, Ekeler, etc.