If Metro Exodus generated the same gross revenue on the Epic Games Store, 4A Games would keep approximately $52,932,787 - that's $7,921,162 more than on Steam.
At this revenue level, Epic's concrete platform fee would be $7,081,744. 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 $42,010,171.
Note: This is a hypothetical comparison. Actual sales volumes differ significantly between platforms, and Steam's larger user base typically drives substantially higher sales.