The Patriots 2008 offensive DVOA after they let Cassel take the training wheels off was almost exactly the same as their 2009 DVOA with Brady (25% range), which is almost exactly the same range as this year, and significantly higher than last year, and falls right in-line with the patriots offensive DVOA most years (+15-35%). There's a strong argument to be made that even if they were similar caliber of players (they aren't) you'd see a decline early just because Cassel had been receiving the minority of the practice snaps. The idea that they were going to be able to maintain 2007 is ridiculous - they couldn't even maintain the pace the whole season. 2007 and 2010 are major outliers, not 2008.Yeah, but the 08 Pats went 11-5 and missed the playoffs as one of only a handful of 11-5 teams to ever do so. And they had the sixth best point differential in the whole NFL that year. It's pretty easy to compare that Pats team to the first non-Jordan Bulls team, I think. It's still a team sport in both cases, no matter how transcendent the one player is.
They didn't miss the playoffs because of Cassel - they missed it because their defense was terrible and landed them in a weird tiebreaker. (from a relative standpoint, the defense declined more than the offence did from 2007->2008 from 8th to 20th)
Here are the second half points scored by the Cassel led offense:
20, 31, 48, 10, 24, 49, 47, 13 - 30 point's per game, and only one game where they were really a problem (loss to Pitt 33-10. 13 point game was a win in terrible weather).
So yes, I absolutely believe that BB will put together a top tier offense post Brady. Will they be historically good like 2007/10? Probably not, but they'll absolutely be consistently top 10 in the league.