If Call of Duty: Black Ops Cold War generated the same gross revenue on the Epic Games Store, Treyarch, Raven Software, High Moon Studios, Beenox, Activision Shanghai, Sledgehammer Games would keep approximately $24,844,542 - that's $4,272,489 more than on Steam.
At this revenue level, Epic's concrete platform fee would be $3,251,528. 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 $19,667,249.
Note: This is a hypothetical comparison. Actual sales volumes differ significantly between platforms, and Steam's larger user base typically drives substantially higher sales.