If The Elder Scrolls V: Skyrim Special Edition generated the same gross revenue on the Epic Games Store, Bethesda Game Studios would keep approximately $169,704,396 - that's $18,536,763 more than on Steam.
At this revenue level, Epic's concrete platform fee would be $23,005,145. 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 $134,896,679.
Note: This is a hypothetical comparison. Actual sales volumes differ significantly between platforms, and Steam's larger user base typically drives substantially higher sales.