Rowan Williams’ conclusions at the end of his fine book (Arius Heresy and Tradition, Eerdemans, 2001) are not a simple historical assessment; they are theological. They have more to do with a transhistorical significance than actual history. They identify what many Christians see as the unique and irreplaceable contribution of Christianity to the religious needs of humankind as they played out in later centuries. One may disagree. Athanasius claimed that Arius’ theology was a pale and bloodless version of the real meaning of the Christ event; redemption was more transcendent than Arius would have us imagine. Arius’ belief that the Logos was a second, lesser and created “god,” according to Athanasius, would fundamentally eliminate the real “God” from the equation and thus obviate theosis (“divinization”).
Arians insisted that they took theosis seriously, but Athanasius “denies that this can be done while still clinging to the idea of a mediatorial created redeemer.”
[Arians] seem to have argued that the creaturely status of the Son did not affect the power of the divine word uttered through him; the agent of redemption remains God alone. Athanasius’ retort is to ask why, in this case should there be an incarnation at all. … The only decisive redemption — as opposed to continual acts of grace and pardon — is the transfiguration of the human condition from within, the union of grace with the body, as Athanasius puts it (con.Ar. II 68). The argument returns to the point of the absolute newness and difference of redeemed humanity; for this newness to make sense, we must suppose a critical rupture in the continuities of the world; and for this God alone is adequate … 
It is important to clarify: the “critical rupture” Williams refers to in this paragraph can only be something that functions like Augustine’s “original sin” recapitulating Platonic substance dualism, i.e., something that drives an “ontological” wedge between humankind and God. And the “transfiguration” mentioned has to be some kind “ontological” repair that makes theosis, “divinization,” more than a metaphor. We know what theosis meant to Athanasius’ Platonic mindset: it meant immortality — setting humankind on the level of the gods, erasing the “unnatural death sentence” incurred by the human material condition aggravated by original sin. It needs to be emphasized: theosis in Athanasius is not just the emotional aspiration of a Christian romantic who feels close to Jesus, it is inextricably part of the cosmology of alienation stemming from Plato’s dualism, reformulated as “original sin” by Paul and Augustine forming the fundamental tradition of Catholic Christianity. We must understand this: they are talking about science: a metaphysical not just a relational or moral rupture. This metaphysical rupture was then “healed” by baptism which created a new ontological bond between God and humankind; they are talking about what for them was cosmology, science, not poetry.
Now, I want to say this and say it very clearly: If there is no dualism dividing matter from spirit, and no “original sin” … if our alienation from “God” is moral and relational and not ontological, then this entire worldview with its many variants falls like a house of cards. None of it makes any sense, philosophically or theologically, except as metaphor, meaningful only to those who understand Platonism. It is not religion, it is a phantasmagorical cosmology. The Jews, who wrote Genesis, reject it unequivocally. They claim that the story of original sin (their story) was not literal, and was intended from the very beginning as simply a fable — an allegory, a catechetical device chosen for its pedagogical ability to illustrate the importance of obeying “God’s” commands and relating to one another morally. Genesis is not a record of scientific and historical “facts.” There was no “critical rupture” in the “continuity” between God and man. Such a theory, even for Paul, was tangential: it was not central to his view of the Christ-event. It was increasingly used to justify the “supernatural” nature of the Christian claims as Platonism came to predominate in the ancient mindset; for as Williams admits in the above citation, without such a supposition Christian soteriology “makes no sense” nor does the incarnation. Indeed!
The view of things officialized in the Nicene version of the incarnation contrasts with the “pagan” religiosity which it was even then displacing. Peter Brown (The Making of Late Antiquity, Harvard, 1978) claims that the Christian vision amounted to “a denial of the ease of access to the supernatural that would have put ‘heavenly’ power in the hands of the average sinful believer.”
Pagans watched this development [the focus on the “other world”] with deep religious anger. For in the “debate on the holy” Late Antique pagan sentiment maintained to the last, one feature of the traditional position: the supernatural was constantly available to men. … the easy-going unity of heaven and earth somehow mirrored the unity and solidarity of the civilization they had inherited, which had passed on to them a richness of well-tried means of access to the other world.
The Jews who wrote Genesis did not have any need for a mediator, like Plato’s “Craftsman,” no matter what its divine pedigree. They were in direct contact with Yahweh at all times because they were his natural creatures, the children he created to share existence with — his family. The theory of a mediator between God and humankind — Plato’s Craftsman, who served as model for the incarnate Word — is Greek and was required by Plato’s substance dualism in order to interface between a Spirit-God and a world of corrupt matter. The theory of the fall is Greek and it was concocted to explain how we came to have a spirit-soul in a body of matter. Philo distorted the Jewish Scriptures in order to have them mesh with Plato’s substance dualism. He took a human fantasy like Plato’s Craftsman in the Timaeus, called it Logos and poetically suggested that it was the “Wisdom” of Proverbs 8, an entity a real person, a subordinate “god.” Christianity then applied Philo’s fantasies to Jesus. Nicaea, by ultimately insisting that Plato’s Craftsman was really the high God himself, ironically eliminated the very mediator that was so important to Plato’s view of the world. It was an indirect hit on substance dualism and while it obviously was not fatal, it introduced a fundamental incoherence into the once tidy Platonic picture that Arius was trying to preserve with his clear and logical explanations.
Brown sees the ancient pagan mysteries as having evoked a different worldview from that of the ascendant “otherworldliness” of fourth century Christianity.
Among the pagans, therefore, the crisis of a great tradition was sensed as nothing less than a crisis in the relations of heaven and earth. … ‘The central claim of the mysteries to authority and legitimacy rested precisely on this complex of correspondences with the nature and order of the cosmos.’ The pagan still expected to feel embedded in this cosmos. The Christians had brutally torn the network of correspondences on which pagan belief depended. Hence the anger with which Plotinus rounded on the Christian-influenced “Gnostics,” who refused to be either humbled or consoled by the majesty of the cosmos.
Brown quotes from Iamblichus of Apamea (+ 327, a follower of Plotinus’ Neoplatonism) lamenting the loss of simple religiosity brought about by the focus on philosophical transcendentalism, an accusation that is applicable to both sides of the Nicene dispute:
… placing the physical presence of the superior beings outside this earth … amounts to saying: the divine is at a distance from the earth and cannot mingle with men; this lower region is a desert, without gods.
I would like to take that accusation seriously and advance an argument for another and entirely different way of conceiving the relationships that were in contention in the Nicene controversy. It is a view that “places humankind correctly against the overwhelming backdrop of the cosmos.”