If Battlefield™ 1 generated the same gross revenue on the Epic Games Store, DICE would keep approximately $131,948,016 - that's $15,104,365 more than on Steam.
At this revenue level, Epic's concrete platform fee would be $17,856,548. 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 $104,863,194.
Note: This is a hypothetical comparison. Actual sales volumes differ significantly between platforms, and Steam's larger user base typically drives substantially higher sales.