Rogers v Bellei did not define natural born citizen. The holding in that appeal was that Congress has the power to impose the condition subsequent of residence in this country on Bellei, who did not come within the Fourteenth Amendment’s definition of citizens as those “born or naturalized in the United States,” and its imposition was not unreasonable, arbitrary, or unlawful. Bellei’s problem was that he did not meet the residence in the U.S. requirement of an 1874 law that applied to his birth circumstances.
I agree with you that the issues of electability and eligibility are completely separate.
In many court decisions it is possible to agree or disagree with the court’s ultimate holding and agree or disagree with the dicta that preceeds the holding.
Time will tell on whether Rogers v Bellei impacts Ted Cruz’s status as a natural born citizen. It obviously had no effect on Barack Obama’s eligibility or electability.
And what you deliberately refuse to acknowledge is that "Natural born citizens" existed before 1874, and for that matter before 1868, and therefore such laws are immaterial to the meaning of the term.