If Octodad: Dadliest Catch generated the same gross revenue on the Epic Games Store, Young Horses would keep approximately $3,654,882 - that's $843,044 more than on Steam.
At this revenue level, Epic's concrete platform fee would be $362,029. 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 $2,811,838.
Note: This is a hypothetical comparison. Actual sales volumes differ significantly between platforms, and Steam's larger user base typically drives substantially higher sales.