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.