Nobody is calling him a system QB and I think Bill proved that last part already in 2008 and the first 4 games of 2016.
Let’s go through 2008
1. virtually the same team as the undefeated 2007 team minus the QB
2. Played 8 teams across two divisions with one 9-7 winning record
3. Dropped 5 games and missed the playoffs
4. Belichick only missed the playoffs three times with the Patriots as a starter. 2000, 2002, 2008. Is it a coincidence that both times he didn’t have Brady he didn’t do it and 17 out of 18 times with him he did?
5. Cassell did make the playoffs on a Todd Haley coached team that was much weaker 2 years later.
Now let’s look at 2016
1. Jimmy Garopollo proved he could lead a team to the SB.
2. He beat a 7-8-1 Cardinals team that only strung two wins together twice all season
3. He beat a good Miami team but he also played lights out that day so I don’t know how much credit you give the coach if a QB who proved after that he was good has a good day.
4. Yes this was the one impressive Belichick performance when the defense shut out a 9-7 Texans squad.
5. Then they got shut out the following week against a Bills team that Brady dropped 41 on.
6. Brady came back and went 14-1 including winning the SB with that team. So.....