IMHO, the "baby" in the bathwater is that the speed of light may have indeed varied as also indicated by the fine structure constant observations.
There is a difference between the (predicted by theory) change of 1/10000 or so since the Big Bang and the 17% over the last few hundred years that Setterfeld claims. Note that should Setterfeld use even older data, the speed would have been estimated as infinited (before the 1600s).