If Totally Accurate Battle Simulator generated the same gross revenue on the Epic Games Store, Landfall would keep approximately $48,175,307 - that's $7,488,664 more than on Steam.
At this revenue level, Epic's concrete platform fee would be $6,432,996. 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 $38,225,812.
Note: This is a hypothetical comparison. Actual sales volumes differ significantly between platforms, and Steam's larger user base typically drives substantially higher sales.