But I believe that proto-Indo-Aryans and proto-Iranians (Aryans) were J2a folks from West Asian that mixed with R1a-Z93 native to the Iranian Plateau and Central Asia! So It makes actually sense that bull-worshiping in Indus Valley is from West Asia, because West Asian/Caucasian y-DNA hg. J2a is present in Indus Valley. Also have you noticed that Indus Valley is very high withGedrosia autDNA component. And Gedrosia component is closely connected to West Asia/Caucasiancomponent.
Well, I respect your own opinion, but I have to say that most genetists are convinced that R1a was the original lineage of Indo-Aryan people (who, indeed, were IE nomads coming from present Turkestan -Adronovo/Sintashta cultures-, keen to proven R1a Tocharian folks), while J2a is thought to be a non-IE lineage that Indo-Aryans later incorporated during their journey to Hindustan through the Iranian plateau. Which seems to be exactly the opposite to what you said
I can't say who's right, but I haven't seen any evidence against the traditional R1a theory, so far.
Besides this, and much more important: Indus Valley civilization is not Indo-Aryan, since it rose much earlier, at about a thousand years before Vedic people reached India. So, even if we consider Aryans to be a middle-eastern J2a cluster, which just met R1a through its way (as you said), cattle worship in India can't be expained as a result of an Aryan invasion from the Tigris, simply because buffaloes were already worshipped in India (or at least had some sacred importance) when Aryans got there.
So, whether Indo-Aryans were J2a or R1a people, it gets unrelevant: cattle worshipping (of some sort) preceeded them of a millenium.