If Total War: ROME REMASTERED generated the same gross revenue on the Epic Games Store, Creative Assembly, Feral Interactive would keep approximately $8,340,401 - that's $1,801,446 more than on Steam.
At this revenue level, Epic's concrete platform fee would be $1,000,964. 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 $6,538,956.
Note: This is a hypothetical comparison. Actual sales volumes differ significantly between platforms, and Steam's larger user base typically drives substantially higher sales.