I think a lot of fans have figured out that simply looking at last year’s win-loss records for this year’s opponents isn’t really a good way to evaluate this year’s strength of schedule. Lots of people have tried to create better ways to evaluate strength of schedule. Some people, for example, look at betting trends in Las Vegas to evaluate the strength of opponents for the upcoming season. Some number crunchers rely on statistical algorithms to project changes from last season in terms of opponent strength.
In the end, with retirements, cuts, injuries, free agency and the draft, teams change so much from one season to the next that it’s very difficult to paint an accurate Strength of Schedule (SoS) picture.