The Sangam-to-Bhakti transition is presented as an epochal rupture, not a studied process.

Evidence

The transition from Sangam to Bhakri, which was also a Tamil phenomenon, is known only in very broad outline, bur nor really as a transition, more as a discrete epochal shift, after a gap of centuries and the intercession of an ‘epic’ tradition. — Aijaz Ahmad, In Theory, 1097