If Call of Duty 4: Modern Warfare (2007) generated the same gross revenue on the Epic Games Store, Infinity Ward would keep approximately $10,783,254 - that's $2,195,253 more than on Steam.
At this revenue level, Epic's concrete platform fee would be $1,334,080. 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 $8,482,134.
Note: This is a hypothetical comparison. Actual sales volumes differ significantly between platforms, and Steam's larger user base typically drives substantially higher sales.