If Streets of Rage 4 generated the same gross revenue on the Epic Games Store, Dotemu, Guard Crush, Lizardcube would keep approximately $10,378,731 - that's $2,135,494 more than on Steam.
At this revenue level, Epic's concrete platform fee would be $1,278,918. 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 $8,160,354.
Note: This is a hypothetical comparison. Actual sales volumes differ significantly between platforms, and Steam's larger user base typically drives substantially higher sales.