If The Quarry generated the same gross revenue on the Epic Games Store, Supermassive Games would keep approximately $24,274,072 - that's $4,188,215 more than on Steam.
At this revenue level, Epic's concrete platform fee would be $3,173,737. 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 $19,213,466.
Note: This is a hypothetical comparison. Actual sales volumes differ significantly between platforms, and Steam's larger user base typically drives substantially higher sales.