If Call to Arms - Gates of Hell: Ostfront generated the same gross revenue on the Epic Games Store, Barbedwire Studios, Digitalmindsoft would keep approximately $17,532,508 - that's $3,192,302 more than on Steam.
At this revenue level, Epic's concrete platform fee would be $2,254,433. 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 $13,850,859.
Note: This is a hypothetical comparison. Actual sales volumes differ significantly between platforms, and Steam's larger user base typically drives substantially higher sales.