My own thinking is similar, yet without Adam and Eve being individuals. I see Adam’s story as telling humanity’s story, and in the one place in Genesis where Adam is split into Adam and Eve, both continue to tell different aspects of humanity’s story. So, my focus on Adam isn’t to discount women, but based on the way Genesis itself uses Adam as an umbrella term for all humans (e.g. Gen. 1:26–27; 5:1–2; 6:3, 5–6, etc.).
But I agree that what Adam (however understood) contributes to sin is the twisting of the environment and culture we’re all born into. That escalating corruption does seem to be a theme in early Genesis, while suggesting the sexual transmission of this corruption seems to go well beyond the text.
I also agree that the Eden narrative doesn’t show us the ultimate origin of evil, as I think @Shawn_Murphy was noting. The serpent is present and acting badly before anyone disobeys. So, because the story isn’t trying to explain the origin of evil, it becomes even less important to view its characters as historical individuals who can be blamed for sin’s origin.