I would expect victors to write down how amazingly stupid their opponents were and why that gives them god given right to now lord over them and their subjects...

you may expect that, but my assumption would be that in most cases condescension and pettiness would fail to trump disinterest and dismissal

I'd almost expect that to be so remarkable as to merit writing it down.

Not really, first, being wiped out doesn't mean literally everyone dying, but also it doesn't prevent the winning side from recording the victory and its cause

Perhaps oral traditions survive from soldiers sold into slavery from lost battles. Like somehow, the folly of volley fire made it into the name of some food dish.

Or maybe they would have simply massacred any army so dumb as to try it.

I don't understand the need to come up with some fancy niche (slavery, oral, food name) when you have the more common approach: as is usual, part of the army ran away, and it included people of all ranks, from soldiers to generals, and they recorded it in all the same ways all the other events for recorded in the same sources (including training guides)

Then you continue to ignore the other elephant - the soldiers and everyone else who won battles also record history avoiding the slavery/food route

And again, "massacre" doesn't mean 100%

A response which could be given just as easily to any claim of the form “X never occurred in human history.”

Occam's Razor.

to me Occam's Razor is a fairly unsound thinking strategy, particularly in scenarios like this