If Age of Empires II (Retired) generated the same gross revenue on the Epic Games Store, Skybox Labs, Hidden Path Entertainment, Ensemble Studios, Forgotten Empires would keep approximately $41,124,588 - that's $6,677,496 more than on Steam.
At this revenue level, Epic's concrete platform fee would be $5,471,535. 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 $32,617,286.
Note: This is a hypothetical comparison. Actual sales volumes differ significantly between platforms, and Steam's larger user base typically drives substantially higher sales.