Well, I really can agree to disagree, so long as I'm not accused of "twisting history" for simply posting direct Patristic Quotations.
Personally, my own sense that when Church Fathers say "Ye are saved by grace through faith, not through works.... that is, by faith alone, as owing nothing to the law" or "Man, by making an ill use of his Free-will, lost both himself and it" or "The Sacraments of the Altar are not the real Body and Blood of Christ, but only the commemoration of his Body and Blood", one may safely assume that they're expressing their genuine beliefs; but, to each his own.
On the other hand, these communities did see themselves as separate from their competitors, the Anglo-Saxons. An early Welsh ecclesiastical rule levied penalties for interacting with the English, and for sharing communion with them. When St Augustine attempted to meet with a delegation of seven British bishops on the borders of the domains of Ethelbert of Kent, these bishops refused to talk or even dine with his party; and when Aethelfrith of Northumbria went to battle with Solomon, son of Cynan, king of Powys, hundreds of British Christian monks are said to have assembled to pray for the Venedotian king. It is noteworthy that the British failed to attempt to convert the Anglo-Saxons, and that the successful Celtic missions had come from further away, from the Dalradian Scots.
That, I do recognize... the Link I posted in #26 dwells at some length on the Anglo-Saxon invasion as the cause by which Bede says the Celtic Orthodox were shut away "beyond the reach of the decrees of synods, . . . they could learn only those thing contained in the writings of the Prophets, the Evangelists, and the Apostles."
It is easy to exaggerate the cohesiveness of the Celtic Christian communities. Their members never saw themselves in opposition to the Catholic establishment based on Rome as did the Arians, Priscillianists or the Donatists in North Africa. Even at the height of the conflict between these communities and other Christian groups, they acknowledged the supremacy of the Pope and acquiesced to his specific commands.
Perhaps... but Columbanus' letter to Boniface does not suggest any unreserved subservience, either -- as just one important example of the Celtic's Church's essential independence of action.