If From the Depths generated the same gross revenue on the Epic Games Store, Brilliant Skies Ltd. would keep approximately $6,913,152 - that's $1,509,508 more than on Steam.
At this revenue level, Epic's concrete platform fee would be $806,339. 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 $5,403,644.
Note: This is a hypothetical comparison. Actual sales volumes differ significantly between platforms, and Steam's larger user base typically drives substantially higher sales.