In regard to point 5) (see the previous post) I agree with Scot that I don’t think the later Christian notion of seminal transmission of a sin nature from Adam is a necessary conclusion from what the Bible says. It is the curse that affects the whole human tribe, not Adam’s sin nature. 6) since all have sinned and lack God’s glory now, it is not necessarily the case that without the historical Adam we don’t need the Gospel of salvation, but I would say that Adam’s sin is the presenting cause which led to the curse which in turn led to fallen human beings.
It is hard for me to doubt that the sorry history of the human race, full of wickedness, bloodshed, hatred, wars etc. is not a profound testimony to sin and fallenness. And besides the Psalmist say in Ps. 51.5—- “surely I was sinful from the time my mother conceived me”. That is hardly a statement about volitional sin after birth. I suspect as well that Paul’s language about ‘flesh’ and his discussion in Rom. 7.14-25 that people can know better, but apart from Christ cannot do the Law, should have some bearing on whether we’ve all ‘fallen’ and can’t get up without redemption.