If Marvel’s Spider-Man: Miles Morales generated the same gross revenue on the Epic Games Store, Insomniac Games, Nixxes Software would keep approximately $45,757,035 - that's $7,268,821 more than on Steam.
At this revenue level, Epic's concrete platform fee would be $6,103,232. 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 $36,302,187.
Note: This is a hypothetical comparison. Actual sales volumes differ significantly between platforms, and Steam's larger user base typically drives substantially higher sales.