I agree and disagree. You can produce rankings based on what has already happened, and it is 100% real data. (There are "standings" from game 1 in the pros and in conference play, knowing that they will change a lot over time) Which of course points out the absurdity of polls before Oct 1. One game does not a season make (unless you're ISU).
Even as the season goes "like opponents" are mostly in conference, and we all know the flaws of that A beat B and B beat C so A should beat C. The best "assumptions" I think you can make are tougher schedules and conferences overall. Sagarin does a pretty good job of incorporating that as the season progresses.
ANYWAY. I like Sagarin's data-grounded method. Which is why I wish he'd stick to it, even early in the season. If Mizzou loses to Wyoming and Wyoming is #71 by Sagarin's own method (even after beating Mizzou)...then Mizzou sure as hell isn't worthy of #36.