If Crypt of the NecroDancer generated the same gross revenue on the Epic Games Store, Brace Yourself Games would keep approximately $7,958,282 - that's $1,723,285 more than on Steam.
At this revenue level, Epic's concrete platform fee would be $948,857. 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 $6,234,997.
Note: This is a hypothetical comparison. Actual sales volumes differ significantly between platforms, and Steam's larger user base typically drives substantially higher sales.