If Tom Clancy's Ghost Recon: Future Soldier generated the same gross revenue on the Epic Games Store, Ubisoft Paris, Red Storm Entertainment would keep approximately $2,875,216 - that's $683,567 more than on Steam.
At this revenue level, Epic's concrete platform fee would be $255,711. 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 $2,191,649.
Note: This is a hypothetical comparison. Actual sales volumes differ significantly between platforms, and Steam's larger user base typically drives substantially higher sales.