If The Elder Scrolls V: Skyrim generated the same gross revenue on the Epic Games Store, Bethesda Game Studios would keep approximately $75,505,490 - that's $9,973,226 more than on Steam.
At this revenue level, Epic's concrete platform fee would be $10,159,840. 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 $59,965,731.
Note: This is a hypothetical comparison. Actual sales volumes differ significantly between platforms, and Steam's larger user base typically drives substantially higher sales.