If Age of Wonders: Planetfall generated the same gross revenue on the Epic Games Store, Triumph Studios would keep approximately $4,539,445 - that's $1,023,977 more than on Steam.
At this revenue level, Epic's concrete platform fee would be $482,652. 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 $3,515,468.
Note: This is a hypothetical comparison. Actual sales volumes differ significantly between platforms, and Steam's larger user base typically drives substantially higher sales.