If Injustice: Gods Among Us Ultimate Edition generated the same gross revenue on the Epic Games Store, NetherRealm Studios, High Voltage Software would keep approximately $8,907,835 - that's $1,917,512 more than on Steam.
At this revenue level, Epic's concrete platform fee would be $1,078,341. 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 $6,990,323.
Note: This is a hypothetical comparison. Actual sales volumes differ significantly between platforms, and Steam's larger user base typically drives substantially higher sales.