Diversity

Theology

Some people equate vaidika religion with indra-centrism and shrauta ritual.

Caution about such - sharauta rituals and Indra’s hymns had a high place in early Aryan religion. Yet, they were not all.

Other practices and theologies (including vigrahArAdhana, shaiva/ vAyavya etc. branches, atimArga ..) were followed in parallel by the very same people. These came to be recorded in later works. Also, vedas refer to non-vedic literature (AkhyAyika-s, purANa-s).

Even within veda-s one sees great diversity in terms of theology (fave/top-Gods) - it’s not “vishvasmAd indra uttaraH” all the time. Same with ritual details, metaphysics etc.. Sometimes such contradictions are acknowledged (with vehemence too!)

Rudra went from being clearly identified with Dyauh Pita to one of the many deities to being completely subsumed by Vayu and Agni to resurging in the late Vedic period

Mythic evolution

This is just plainly apparent when looking at the TS or MS and then the Brahmanas describing the same deed (Indra feeding the Yatis to the Salavrkeyas; the former praise it on par with Indra slaying Vritra, the latter list it as one of Indras sins).

Indra being ritually excluded from soma consumption just because he killed someone and came in contact with blood (thus becoming ritually impure) IS a evolution of Vedic thought itself. Show me even an inkling of such an idea in the early RV. This is what Jameison says as well

Ritual evolution

In the RV they were beheading in the sacrifices.
Aryans started seeing blood + death as impure and contact with blood or death in ritual led to so much ritual impurity you would become ineligible to drink Soma. This is the reason that sacrificial animals are choked on the yupa.

Epistemology

There is inter-shAkhA rivalry. See shAkhA-spardhA