I get what you are saying and there is truth to it but winning in the playoffs is a hard thing. You have to give him credit for his total body of work. Those 9 times were years his team made the playoffs, plus all the others where he advanced. His team made it to 4 SB's with 4 different coaches. In all cases that is the only SB for the head coach. Brady has Belicheck
If you look at Bradys post season stats as compared with regular season since 2005 you see a pretty big drop off just like Manning if you look at TD's/INT's, rating. Both QB's are 2-2 in the SB since 2005. I say since 2005 because the teams Brady was on in 2001-2004 were very different, Brady's role on those teams was very different.
Manning played Brady 4 times in the AFC Championship game and won three. People don't seem to know that stat, instead there is this perception that the Patriots owned Brady in the playoffs which is not true. Since 2005 they have played pretty even but Peyton was 3-0 in the playoffs.
Having said all that, I would say Brady is better than Manning. I just think there are arguments in Mannings favor and its not as lopsided as a lot assume.