Do the Fathers lead logically to the full-blown theology of the Roman Catholic Church or Eastern Orthodoxy?
Not at all: Epiphanius of Salamis condemned the use of icons and pictures; Cyprian described Stephen, the bishop of Rome, as the Antichrist; Augustine’s view of the presence of Christ is much closer to Luther than Trent; and on and on. Read Calvin’s Institutes and see how often he cites the Fathers, especially Augustine.
And why? Because he believed they supported him, not the Roman Church. And he was right. Again, Thomas Cranmer, the theological and liturgical architect of Anglicanism, was one of the leading patristic scholars of his day, and used patristic sources to construct one of the great books of Reformation piety, The Book of Common Prayer.
No, the Fathers are not necessarily the root of the Roman Catholic Church or Eastern Orthodoxy. They are just as much my Fathers as they are theirs—and I, a full-blown unrepentant Evangelical—am not ashamed to own them as my theological mentors and forebears. Of course, this does not mean I believe everything they believed, even as I do not believe everything my great hero Andrew Fuller believed—e.g., his view that John Wesley was a crypto-Jesuit is plainly ridiculous 😊.
So, obey the command given to Augustine: tolle lege—read the Fathers!