If Ultimate Epic Battle Simulator generated the same gross revenue on the Epic Games Store, Brilliant Game Studios would keep approximately $4,351,068 - that's $985,446 more than on Steam.
At this revenue level, Epic's concrete platform fee would be $456,964. 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 $3,365,622.
Note: This is a hypothetical comparison. Actual sales volumes differ significantly between platforms, and Steam's larger user base typically drives substantially higher sales.