What do you mean by unbelief and rejection of personal God? Prophets do not qualify here, and yet they also had a problem understanding.
Life will become more difficult, but where and how exactly is the Sin passed along? …Only with Paul comes the idea that newborn babies have no more free will and choice to be righteous or sinful, but are condemned right from the start, with the sin mysteriously passed from Adam onto them. In Genesis, God curses Adam, Eve and the snake, but note the consequences for Adam were that growing food will be difficult from now on and death will be a fact of life. Not a hint about all humanity will be born sinful by default, with their free will suspended. And hence prophets struggling to cope with the problem all the time. They never knew about the original Sin. And no one did, until Paul.
In fact, when God later says “I will be their God, and they shall be my people”, what does it mean? Isn’t this a covenant after the “Original Sin”, and a hope for righteous to be protected if they chose so?
Finally, I will quote your own words: “As created with free-will, it is mankind’s sin which is the root of all evil.” But now you follow the suit of the prophets, you also struggle to find the explanation, and when mankind could not do the job, you pin it down to Adam. If all mankind abused free will, that would explain why innocents suffer. Only, innocents never had an opportunity to entertain their free will. ( this again fails to answer the cause of natural suffering ) But wait, with your new explanation, innocents are now stained with sin, through Adam. Do try again, I came up with five options, none of them working.
Well, it is me and the prophets. I guess I am in the good company