It’s something of a canard for people trying to argue why their team is better or—more to the point—someone else’s team is worse to point to the other team’s lack of scheduling appropriately tough foes and rolling up their record on creampuffs. There’s definitely no foolproof way of measuring strength of schedule, be it preseason rankings, in-season rankings, end-of-season rankings, advanced stats and projections of how a team should have performed in terms of wins and losses (regardless of actual results on the field) and on down the list.
We have vastly more data available now than ever before, especially in advanced metrics, but even in terms of simple rankings the gold standard for college football, the AP poll.