I don’t know much of the field of rationality, yet I can’t help but think that you confirm my idea that rationality is subjective. You determine rationality based on probability, so essentially when you’re saying something is irrational, you mean it is improbable (or in your words realistic).

Taken further, is it not then irrational to think that the earth arose out of absolute nothingness, to become the perfectly aligned world we know? Is this realistic? Is this probable? (Not saying the alternative is necessarily more probable, just asking)

As to your default sentence you might want to look into the discipline of Harmatiology (the doctrine of sin), for you do not understand the commonly held view of Christians on this point.