I think you're ignoring the meaning and history of the word "epic". For one thing, it comes from a time when cities and armies were thousands instead of million

I think you're ignoring the meaning and history of the word "epic". For one thing, it comes from a time when cities and armies were thousands instead of millions, and for another, it just never was based on some specific numeric scale. One description is: "...involving a time...in which occurred the extraordinary doings of the extraordinary men and women who, in dealings with the gods or other superhuman forces, gave shape to the moral universe for their descendants...to understand themselves as a people or nation"