If Total War: ROME II - Emperor Edition generated the same gross revenue on the Epic Games Store, CREATIVE ASSEMBLY, Feral Interactive would keep approximately $101,825,580 - that's $12,365,962 more than on Steam.
At this revenue level, Epic's concrete platform fee would be $13,748,943. Epic charges 0% on the first $1 million in annual per-app revenue and then 12% on the remaining amount. On GOG (30% cut), the developer would earn approximately $80,902,166.
Note: This is a hypothetical comparison. Actual sales volumes differ significantly between platforms, and Steam's larger user base typically drives substantially higher sales.