The problem with this argument is that it is looking at Scripture backwards, from the present, and it makes the same mistakes we condemn the Jehovah's Witnesses for making.
1. Original Sin is a post-Biblical concept introduced by Irenaeus, Bishop of Lyon of the 2nd century. You have to read that into Pauline theology as it is not native to it. There is no "original sin" native to Scripture without Irenaeus and the Catholic Church.
2. The "Bible" is not one "book." It is the library of two separate religions who use it for two separate purposes and have two different and very unique interpretations of the Hebrew portion of the text (which is the majority of the Bible). One therefore cannot claim there is any particular "theme" or "essence" without first supplying a Jewish or Christian background for the assemblage of the separate canons: the Old Testament on one side and the Tanakh on the other.
Even from my Jewish point of view, the New Testament is not claiming that Jesus has ransomed people from death by his own dying. This is a peculiar Watchtower teaching taken from Adventist ideas. The New Testament is teaching that Jesus has offered his Divine Life as "food" not to God but to humanity, much like God offered manna from heaven to people, to supply "divine life" to those who partake of his sacrifice as a communion or Passover meal.
The ransom idea of the Watchtower is an odd focus and holdover from Russell's era. The word does occur in the Greek text but it is a play on the Hebrew word "redeem" in reference to the Exodus. The Jews were redeemed from slavery, figuratively "purchased" from one sovereign by another. The "ransom" was the miraculous hand of God and the events of the Exodus that redeemed the Jews from slavery.
This is the meaning of Christ's "ransom" in the New Testament, a redemption from slavery to sin's captivity to death. The Watchtower theology is a twisting of this that is sometimes found in other Adventist branches but never in Catholicism, Orthodoxy, or mainstream Protestantism. One would even be hard-pressed to find the Watchtower view in Fundamentalist churches.
The Watchtower teaches that a life was offered to God to balance the scales of justice. The New Testament teaches that Jesus sacrificed his life as an offering for humanity, that they might partake of it and gain the eternal life that it is endowed with and he gives to any who eats of it.
Like the Jewish prophets of the Hebrew Bible stated, God does not require the blood of sacrifices or needs to be appeased with any gifts any human can offer God because everything already belongs to God.