[Jap2-0]

> There's no evidence of it in contexts where we would expect something like this to be mentioned.

What are those contexts?

[margalabargala]

Firsthand accounts of battles involving massed archers.

[matusp]

I think the most obvious context is visual art. There are thousands of depictions of medieval battles. Would really nobody think of depicting a volley of arrows in any of them? That would be a pretty spectacular sight with supposedly devastating effect.