If Total War: WARHAMMER generated the same gross revenue on the Epic Games Store, CREATIVE ASSEMBLY, Feral Interactive (Linux), Feral Interactive (Mac) would keep approximately $60,587,603 - that's $8,617,055 more than on Steam.
At this revenue level, Epic's concrete platform fee would be $8,125,582. 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 $48,099,229.
Note: This is a hypothetical comparison. Actual sales volumes differ significantly between platforms, and Steam's larger user base typically drives substantially higher sales.