If Iratus: Lord of the Dead generated the same gross revenue on the Epic Games Store, Unfrozen would keep approximately $4,064,094 - that's $926,746 more than on Steam.
At this revenue level, Epic's concrete platform fee would be $417,831. 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 $3,137,347.
Note: This is a hypothetical comparison. Actual sales volumes differ significantly between platforms, and Steam's larger user base typically drives substantially higher sales.