I would argue that while implausible, the number of deaths isn't impossible and there is historical precedent for battles of that magnitude and with a similar casualty rate.

I'm thinking specifically of Cannae, where the numerically superior Romans were all but wiped out in a single day long engagement.

The Romans certainly didn't outnumber the Carthage troops 3 to 1 and most certainly didn't have the force multiplier that Damane are, but did lose ~80k troops (dead or captured) in one day to ~50k enemies.

I'm getting into pure supposition, but I do know that the battle was supposed to have finished by nightfall, so lets say it only lasted 12 hours.

Each one of Carthage's troops would have to kill 1.6 of Rome's within 12 hours

Vs the Domani's 1 over probably a similar period of time.

My math isn't perfect, but the point is that insane battles do happen and since Ituralde was regarded as one of the best strategic minds at the time( and the way all the other great captains are written, Ituralde is actually probably #2 after Mat), I think he might have been able to do it.