If Skul: The Hero Slayer generated the same gross revenue on the Epic Games Store, SOUTHPAW GAMES would keep approximately $23,220,320 - that's $4,032,547 more than on Steam.
At this revenue level, Epic's concrete platform fee would be $3,030,044. 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 $18,375,255.
Note: This is a hypothetical comparison. Actual sales volumes differ significantly between platforms, and Steam's larger user base typically drives substantially higher sales.