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)

It is paganism that I consider to be the derogatory and misleading word. Calling it paganism was and is a vile attempt to suppress the local religions, whether you consider them derived from PIE or not.

Yes, they were not not overarching, mandatory systems of belief, but is not an excuse to dismiss them as religions. The religions were real. After all, we see the same continuing religious beliefs that you noted (sacrifices, festivals, veneration, etc.) in Hinduism, which traces a direct chain to the PIE religion.