In this thread, u/Iguana_on_a_stick says that 5% casualty rate was on the upper side of normal for a battle during the Roman Empire, and that 2-5% were the norm as per the ancient sources.
Is this a common average across time? It seems like with the advent of gunpowder, and then modern, mechanized warfare these numbers might get higher.
And did place make a difference? Were these numbers the same for Han China, for instance, or the Aztec?
Your question is rather broad. You may have better luck asking about specific times and periods.
I'll just quickly clarify that my figures indeed are only meant to apply to ancient warfare in Europe. Indeed, my sources specifically contrast these figures with much higher attrition rates in the era of gunpowder-warfare, though I can't give you any specifics on what casualties in the early-modern period were.
Furthermore, as I later clarified in the post you linked, these figures refer to the number of deaths^* during the actual fighting, not the total number of people who would die as a result of a battle. So the rate would generally apply to the losses for the victor, not the defeated party.
The loser of such battles would suffer many more casualties, as the defeated warriors would be cut down as they ran away, and then would be pursued by the enemy for many miles.
^* In modern sources, "casualties" usually refers to "dead or wounded" i.e. people taken out of the fight. Ancient sources generally aren't helpful in making that distinction. They list the number of dead and then talk about "many wounds" in vague terms. Therefore, ancient historians often seem to use the word "casualties" to refer to the number of dead, since that's the only figure we have.