If Age of Empires IV: Anniversary Edition generated the same gross revenue on the Epic Games Store, World's Edge, Relic Entertainment, Forgotten Empires, Climax Studios would keep approximately $66,997,873 - that's $9,199,807 more than on Steam.
At this revenue level, Epic's concrete platform fee would be $8,999,710. 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 $53,198,308.
Note: This is a hypothetical comparison. Actual sales volumes differ significantly between platforms, and Steam's larger user base typically drives substantially higher sales.