To begin with, I want to advocate that Christianity is falsifiable. However, this is not how to falsify Christianity. The argument suggests that just because Adam and Eve are fictitious Christianity is false. Well, that doesn’t follow. Even if Adam and Eve are theological myth or allegorical, say, of all humanity, then atonement still applies. This argument is against the theory of universal sin, primarily seminal and original sin (maybe an entailment against atonement). If theistic evolution is true and Adam and Eve are theological myth, Christianity is still true. Paul, in 1 Cor. 15.17, says that if Christ had not been raised from the dead then our faith is in vain. If Christ had not risen then Christianity is not true. That’s the task for falsifying Christianity. This “one fell swoop” argument is not an argument against Christianity at all. What they are arguing against is the model of sin (original sin, imputation, inherited, etc.) and an entailment, at best, would be against atonement. This is an embarrassing argument and demonstrates a complete lack of familiarity with the biblical text, doctrine, and, I know it’s harsh, logic.