The sanctity of an individual is not always related to the accuracy of his theology. I believe that Augustine was in error on a great many things, and also that he always struggled against his Manichaean past, but the churches have always been able to look beyond such things. The Irish read Augustine, for instance, but just ignored all his writing on predestination.
Personally I always side with St John Cassian and do think that some of Augustine's views have had a lastingly negative effect on Western Christianity.
Father Peter