I agree expansion makes the graph harder, though not impossible, to interpret because of expansion. But comparing the relative success of the Cowboys and Vikings to the Saints and Falcons struggles is right there. All the AFL totals are in there so the Patriots, Oilers and Chargers, etc. can be compared.
But it gives you a very good sense of who has sustained success (Bears and Packers) who has been mediocre for a LONG time (Bears then Giants-even with 5 Super Bowl wins between them) and the expansion teams who rise above all others, the Browns, and the single biggest era jump in the chart, Walsh's 49ers. Unless you want to give full credence to the AAFC, in which case I think the Browns increased their overall margin nearly by nearly 3,000 points in slightly less time than Walsh and the 49ers did.