Who brahmanized India?

I am no expert on traditional Indian medicine, but I happened to read an interesting essay (Dagmar Benner's Saṃskāras in Vāgbhaṭa's Aṣṭāṅgahṛdayasaṃhitā) discussing the general theme of the brahmanization of an (originally) non-brahmanical cultural lore. I remember Karin Preisendanz making the same point on the insertion of Brahmanic initiation rituals within the Carakasaṃhitā: such rituals –she explained– are not genuine brahmanic ones, rather they are brahmanizes ones. They have been inserted at a later point of the transmission of the text in order to make it more acceptable to a brahmanic audience. In sum, medicine was not originally part of the brahmanic culture and was brahmanized only at a later point. The same holds true for Atharvaveda (which can be seen as a distant antecedent of medical texts in India). But something like that could also be said in regard to the insertion of Vedic themes (such as vedaprāmāṇya in general) in Sāṅkhya and Vaiśeṣika philosophy. It seems that Indian culture was much more varied at an older time. Is this at all possible? And how did Brahmans gain enough power as to make the rest of Indian culture be influenced by them (although –more often than not– they were not the rulers of the various Indian kingdoms)?