Watkins wrote his magnum opus on The serpent-slaying myth. You might also like ML West's Indo European Myth and Poetry. So the heroic poetry, mannerbund, the specific characteristics of the King of the Gods who is often associated with both wisdom and war, guest hospitality norms, shared characteristics of epic mythology, the myth of stealing mead / ambrosia. There certainly existed a PIE religion.

I don't question your credentials but I also think many things deemed to be IIr innovations may not even be. IIr came through CW -> Sintashta after all and BMAC influences are overstated. For instance, Soma may have a root in this region, but the myth associated with theft of divine intoxicating drink and it's function as the mead of poetry must predate the specific IIr Soma cult.

Maybe tangential (and I agree with you), but “religion” is also a misleading word for many of the practices that Christianity later grouped together as “paganism.”

Where these practices often differed strongly from Christianity was that they were not totalizing, overarching, mandatory systems of belief. They were more about practices embedded in daily and civic life -- sacrifices, festivals, acts of veneration, etc. -- than about belief or internal mental state (“Whosoever believeth in him should not perish, but have everlasting life”). They were also generally quite willing to incorporate gods, heroes, and practices from other peoples encountered along the way.

IMHO, exclusive, universal, doctrinally policed religion developed partly through the interaction of monotheistic traditions with imperial states, which had strong reasons to standardize institutions and identities; although neither Rome nor the caliphates ever achieved simple religious homogeneity.

(And yeah, clearly there's a lot of commonality between many of the cultures derived from early Indo-European migration etc but also incredible diversity and very clear adaptations to wherever they ended up and who they ended up co-existing with)

The "PIE religion" is the name scholars give to the religious pool that is partially reconstructed from the overlapping evidence (poetry+rituals+myth+gods+vocabulary) of its descendants.

Each descendant subregion of PIE of course imposed its own religious beliefs and local gods. There is no surprise there. The key thread of derivative localized polytheism, often rooted in the same nature-based phenomenon, however persisted across the regions.

Refer to the sibling comment by drivers99. Sky god is not a vague lexeme; it is a critical rooting evidence. You're fooling no one by attempting to cover it up. A shallow dismissal of valid evidence is an attribute of a conman.

And then there is Tuesday, for the forgotten god.