If The Sims™ 3 generated the same gross revenue on the Epic Games Store, The Sims Studio would keep approximately $10,743,980 - that's $2,189,452 more than on Steam.
At this revenue level, Epic's concrete platform fee would be $1,328,725. 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 $8,450,893.
Note: This is a hypothetical comparison. Actual sales volumes differ significantly between platforms, and Steam's larger user base typically drives substantially higher sales.