The problem with the Brown's analogies is that he is comparing apples to oranges.
Neither Bledsoe nor the Patriots were performing well when Brady took over in 2001. With Bledsoe under center the Pats had lost 13 of their last 18 games and nine of their last twelve. When Kyle Arrington was pulled it was because he was playing poorly at the time, giving Malcolm Butler an opportunity.
Brady on the other hand is not playing poorly, nor is the team performing badly with him on the field. The worst the team has done in any of the last five seasons - think about this for a moment - has been a loss in the conference championship game! Last year Brady led the NFL in both touchdown passes and lowest interception percentage: two polar opposite metrics. The previous season he was the Super Bowl MVP and the year before that he led the NFL in both 4th quarter comebacks and game winning drives.
The comparison of Brady to Bledsoe or Arrington is a failed grasping at straws. Eventually his skills will deteriorate whether it be due to injuries or age, but until that happens there is no valid reason to replace him - regardless of how well Garoppolo might hypothetically perform in September.