If Call of Duty: Modern Warfare 2 (2009) generated the same gross revenue on the Epic Games Store, Infinity Ward would keep approximately $24,573,916 - that's $4,232,510 more than on Steam.
At this revenue level, Epic's concrete platform fee would be $3,214,625. 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 $19,451,978.
Note: This is a hypothetical comparison. Actual sales volumes differ significantly between platforms, and Steam's larger user base typically drives substantially higher sales.