If Wargame: Red Dragon generated the same gross revenue on the Epic Games Store, Eugen Systems would keep approximately $13,302,742 - that's $2,567,450 more than on Steam.
At this revenue level, Epic's concrete platform fee would be $1,677,647. 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 $10,486,272.
Note: This is a hypothetical comparison. Actual sales volumes differ significantly between platforms, and Steam's larger user base typically drives substantially higher sales.