Your analysis is based off the Patriots playing a 3-4: how much have they played a 3-4 in the preseason thus far? Four drives over two games?
Your analysis would be better if you considered it within the defense that the Pats are actually playing, one that had Bruschi as a second-string MLB in the first three preseason games. In that case, Bruschi has a hard time making the roster without any special teams impact.
In the preseason, the Pats defense has almost exclusively looked like this, excluding injuries:
SLB: Thomas, MLB: Mayo, WLB: Guyton
SLB: Woods, MLB: Bruschi, WLB: Lenon/Crable
SLB: Alexander, MLB: Ciurciu, WLB: (Tank)
Early downs:
LDE: Warren, LDT: Wright, RDT: Wilfork, RDE: Seymour
LDE: S. Williams/(L. Smith), LDT: Pryor/Richard, RDT: Brace/Adams, RDE: Green
Passing downs:
LDE: Burgess, LDT: Green, RDT: Seymour, RDE: Banta-Cain/Ninkovich