The take-home message here is that Pelagius was a good, sharp guy -- though one who was completely wrong, in my opinion. Those of us on the Reformed side of the equation cannot turn Pelagius (or Arminius) into the epitome of evil. Pelagius was probably a good guy.
This state of things is not without other parallels. Any orthodox Christian would consider Albert Schweitzer's "Historical Jesus" downright heretical. But his medical work in Africa earned him a well-deserved Nobel Peace Prize.
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.