I am using arbitrary numbers to illustrate the point, luckily Epic doesn’t actually have to guess what an appropriate fee would be: They let this guy run wild for months so they know exactly how much revenue he generated, and they know how much of a fee they would need to introduce in order to ensure that this behavior would be unprofitable.
This is also not “speculation”. Internalizing costs of negative externalities is basic economic practice, it’s extensively studied and known to work.
What we don’t know, is if Epic can actually effectively police content. They haven’t managed to do it so far… and I take no comfort in being told “well it’s a difficult task”