I'm particularly concerned with Augustine's failed mission on behalf of Rome to incorporate the Celtic Church.
The period of peace that followed the British defeat of the Saxons at Mons Badonicus (c.500) once again allowed for growth of the Celtic Church (especially through the work of St. Columba), although isolation from the Continent continued until the mission of St. Augustine. Having converted King Æthelbert of Kent to Christianity, St. Augustine attempted to convince the leaders of the Celtic Church to change those practices (such as the dating of Easter and the forms of baptism and tonsure) that were at variance with the Roman Church and to accept the imposition of a diocesan organization on the essentially monastic structure of their church. He failed, and it was not until the Synod of Whitby (664, see Whitby, Synod of) that such agreement was largely reached, although independent Celtic churches continued on in Wales and Ireland. See J. T. McNeil, The Celtic Churches (1974); F. E. Warren, The Liturgy and Ritual of the Celtic Church (1987).
I fear that Augustine (who was human, I think....and sinful) might over over-stated his case for personal reasons.
That's the whole point of The Confessions. The conversion of a man caught up in the cults of the day who prayed, "Give me purity and continence, but not yet" so that he would become a Saint and Doctor of the Church.
Could Augustine have overstated his case? Perhaps. He did it before with the Donatist controversy when he took "compel them to come to the feast" and used that to justify closing the Donatist churches by military intervention.