If Sherlock Holmes: The Devil's Daughter generated the same gross revenue on the Epic Games Store, Frogwares would keep approximately $6,639,055 - that's $1,453,443 more than on Steam.
At this revenue level, Epic's concrete platform fee would be $768,962. 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 $5,185,612.
Note: This is a hypothetical comparison. Actual sales volumes differ significantly between platforms, and Steam's larger user base typically drives substantially higher sales.