If Battle Brothers generated the same gross revenue on the Epic Games Store, Overhype Studios would keep approximately $10,185,044 - that's $2,106,881 more than on Steam.
At this revenue level, Epic's concrete platform fee would be $1,252,506. 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 $8,006,285.
Note: This is a hypothetical comparison. Actual sales volumes differ significantly between platforms, and Steam's larger user base typically drives substantially higher sales.