If Mount & Blade II: Bannerlord generated the same gross revenue on the Epic Games Store, TaleWorlds Entertainment would keep approximately $211,779,167 - that's $22,361,742 more than on Steam.
At this revenue level, Epic's concrete platform fee would be $28,742,614. 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 $168,365,246.
Note: This is a hypothetical comparison. Actual sales volumes differ significantly between platforms, and Steam's larger user base typically drives substantially higher sales.