how BAD the worst teams are to be useful indicators of anything. To a modestly good team, much less a potential playoff contender, there is no difference between playing New Mexico State and playing Northern Illinois. Either way, you're going win handily and you could win with your second string.

However, New Mexico State is 55 spots lower than Northern Illinois in Sagarin (which I think is flawed but I'll use it for sake of argument).

Here's the problem. The difference between No. Illinois and NM State shows up in schedule strength rankings as the difference between playing Ohio State and BYU. It is NOT. It is basically the same game-- a "gimme." So why do we treat the gap the same?

And that's why the "rankings" are not a relevant measure of schedule strength in real life. That's why you are never going to convince anyone using a schedule strength number that BYU's schedule so far (ranked 12th) has ACTUALLY been harder than, say, Utah's (ranked 40th).
In fact it's absurd to claim that. Which schedule would YOU rather play? Which one would be most likely to result in one or more losses?