Bede's representation of Gildas as a ‘doleful historian’ created an emphasis on the De excidio that has overshadowed the contribution of the letter to Finnian. The outcome has been a preference for the polemical and judgemental image drawn from the De excidio, one that overlooks the moderate and judicious image remembered in the fragmenta. This preferred aspect has, in turn, subtly legitimised Bede's construction of a dark age ca 450–600, perpetuating notions of disorganisation and fragmentation in the Insular church. The image of Gildas Historicus, upheld by Bede as the most significant witness to a political and ecclesiastical rupture in Britain in the fifth and sixth centuries, has cultivated an understanding of the De excidio as a negative and unsuccessful intervention.

Yet clearly, from an Irish perspective, the image of Gildas Sapiens as an expert in canon law implies a memory of the De excidio as a positive and successful intervention that established Gildas as an authority. The De excidio of Gildas Sapiens emphasises his immediate concerns: the providential history of Book I foregrounds the divine favour contingent on accepting his plea for a return to proper Christian governance; Books II and III detail the discrepancies between the contemporary behaviours of kings and clerics and biblical expectations, simultaneously criticising and legitimising these roles as crucial to good Christian governance. The immediate problem for Gildas was how to defend his model of authority without having the formal standing in which to articulate it. He makes clear the challenge he faced:

Gildas's criticisms of his seniors were forged from an acknowledged position outside the established order.