When we pick and choose from data, we can compile whatever fantasy we want. It's not that difficult, especially when you realize your math gives equal weight to 1st and 7th round picks when it comes to developing starters.
As for individual decisions, it's easy to look back on any draft and declare everyone stupid for not taking a certain player. Every team passed on Tom Brady multiple times, including us. So to say the Pats screwed up by not taking player x can be accurate, yet entirely misleading since a lot of other teams passed as well. Everyone screwed up, multiple times. But if you only look at one team's decisions without the others, you get very jaded, skewed data. Which you seem to prefer.
In 2005, we could have had Frank Gore or some other nice players instead of Ellis Hobbs and some spare parts. That ignores the fact that every team passed on guys like Gore multiple times, not just us.
The 49ers should have taken Gore over Alex Smith at #1. In fact, I'd rather have Gore than half that first round, which includes Benson (who was a bust in Chicago), Cadillac, Pacman Jones, Troy Williamson, Mike Williams, David Pollack, Erasmus James, Alex Barron, Matt Jones, Fabian Washington, Marlin Jackson, or Mike Patterson. All were 1st round picks taken by other teams. A lot of those teams would miss again in the 2nd.
Yet you're obsessed with the Pats not taking him at 64. Yes, we should have taken him at 64. In fact, we should have taken him at 32. But the only reason he was even available in the 3rd round was because EVERYONE missed the boat on him. Several times.
In 2006, we should have taken Jennings. But a lot of teams passed on Jennings, including Green Bay, who took Daryn Colledge 5 spots ahead of Jennings. If they really knew what Jennings could be, would they have risked that? Minnesota had two picks between when Colledge and Jennings were drafted. They had a need at WR and very easily could have scooped him up but didn't. So the Packers made a good choice, but they were also very lucky no one else took him first. They almost made a big mistake but got away with it.
The 2007 draft was weak, which is why we traded so many picks. But for all the jokes about Kareem Brown, look at that 4th round and tell me who you would have taken really. The only two guys in that round who have gone onto a Pro Bowl were a long snapper and a fullback. Overall, it was a mediocre draft for everyone, not just the Pats.
2008 might have been the worst Pats draft, I agree. But there were many misses by many teams. Faulting us for not taking Biermann ignores the fact that every team ignored him numerous times. Gholston, Derrick Harvey, Lawrence Jackson, Philip Merling, Quentin Groves, Chris Ellis, Bryan Smith, and Jeremy Thompson were some of the DEs taken ahead of Biermann.
Like any area of team-building like FA or trades, the draft isn't perfect. But in terms of money spent to output, it's an invaluable resource. If a few 6th or 7th rounders don't become starters, that doesn't make the entire exercise a failure.
It also ignores the fact that most of the players you want to pursue in trades/FA signings were draft picks. It stands to reason that getting them when they're at their cheapest is an incredible value compared to signing them at their highest contract points later.