If Assassin’s Creed Rogue generated the same gross revenue on the Epic Games Store, Ubisoft Sofia, Ubisoft Kiev would keep approximately $8,393,436 - that's $1,812,294 more than on Steam.
At this revenue level, Epic's concrete platform fee would be $1,008,196. 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 $6,581,143.
Note: This is a hypothetical comparison. Actual sales volumes differ significantly between platforms, and Steam's larger user base typically drives substantially higher sales.