If Assassin's Creed® Syndicate generated the same gross revenue on the Epic Games Store, Ubisoft Quebec, in collaboration with Ubisoft Annecy, Bucharest, Kiev, Montreal, Montpellier, Shanghai, Singapore, Sofia, Toronto studios would keep approximately $12,907,138 - that's $2,509,009 more than on Steam.
At this revenue level, Epic's concrete platform fee would be $1,623,701. 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 $10,171,587.
Note: This is a hypothetical comparison. Actual sales volumes differ significantly between platforms, and Steam's larger user base typically drives substantially higher sales.