That's fair, but it's also what makes all of this offseason speculation kinda meaningless. I agree that the edge should always go to the unit that's shown that it can go out on the field and get it done together, but I also think that improvements need to be accounted for when they're clearly made. We're all just projecting at this point, and going with what we expect that we'll see once the season starts. It's a balancing act, and everyone weights it differently, and that's part of the debate.
In general, I like to deal with it by assuming that there will be some drop in production, but that it will remain roughly in-line with the role in question and past production in similar roles. For example, I feel comfortable assuming that Lloyd will produce at least on par with his 2011 numbers, that Gaffney will be superior to Branch, and that as a side effect of this Welker's and Gronk's numbers will dip, while Hernandez's stay about level if he remains healthy, and dip if he doesn't.
Based on this, I would agree with a general assessment that the best four passing offenses in the NFL are currently New England, Green Bay, New Orleans, and Pittsburgh. Of those, I think that the Packers' receiving corps is the worst of the four, because after you get past their top two options they're not even close to the other 3 in terms of depth. I'd probably rank the Steelers #3 because they lack the game-changing tight end that you get with New Orleans or New England. As far as ranking the Saints vs. the Pats, it all depends, as you said, on how well the end product comes together on the field. The Pats probably have a higher ceiling, considering what they were able to do last year with nobody to threaten defenses vertically, but the Saints have already done it. I understand the merits of going with either one.