If Total War: THREE KINGDOMS generated the same gross revenue on the Epic Games Store, CREATIVE ASSEMBLY, Feral Interactive (Mac), Feral Interactive (Linux) would keep approximately $130,193,406 - that's $14,944,855 more than on Steam.
At this revenue level, Epic's concrete platform fee would be $17,617,283. 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 $103,467,482.
Note: This is a hypothetical comparison. Actual sales volumes differ significantly between platforms, and Steam's larger user base typically drives substantially higher sales.