I just read the fact about the collections of literature on Wikipedia. I imagine the connections between Persian and Sanskrit must have been well known, whereas similarities in Greek and Persian I'm guessing went largely unnoticed or were attributed to cultural osmosis (based on my shoddy knowledge of both), but what about Sanskrit and the Western Indo-European languages?
If not, what eventually spurred the PIE hypothesis in the West?
If I were a betting man, I d say that even if the claim were true, all of the texts would have been translated in the Persian - the “lingua franca” of the time and region. So I d say it’s unlikely that they would have remarked upon it.
To remake on a tangent, old Persian of Avesta and Sanskrit of rig Veda sound too similar. And yet I am not sure if people knew this back then. Can someone remark upon this?