If Goat Simulator 3 generated the same gross revenue on the Epic Games Store, Coffee Stain North would keep approximately $7,008,417 - that's $1,528,994 more than on Steam.
At this revenue level, Epic's concrete platform fee would be $819,330. 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 $5,479,423.
Note: This is a hypothetical comparison. Actual sales volumes differ significantly between platforms, and Steam's larger user base typically drives substantially higher sales.