If The Elder Scrolls III: Morrowind® Game of the Year Edition generated the same gross revenue on the Epic Games Store, Bethesda Game Studios would keep approximately $5,246,517 - that's $1,168,606 more than on Steam.
At this revenue level, Epic's concrete platform fee would be $579,070. 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 $4,077,911.
Note: This is a hypothetical comparison. Actual sales volumes differ significantly between platforms, and Steam's larger user base typically drives substantially higher sales.