If Far Cry® Primal generated the same gross revenue on the Epic Games Store, Ubisoft would keep approximately $14,291,452 - that's $2,713,510 more than on Steam.
At this revenue level, Epic's concrete platform fee would be $1,812,471. 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 $11,272,746.
Note: This is a hypothetical comparison. Actual sales volumes differ significantly between platforms, and Steam's larger user base typically drives substantially higher sales.