If Europa Universalis IV generated the same gross revenue on the Epic Games Store, Paradox Development Studio would keep approximately $107,734,943 - that's $12,903,177 more than on Steam.
At this revenue level, Epic's concrete platform fee would be $14,554,765. 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 $85,602,795.
Note: This is a hypothetical comparison. Actual sales volumes differ significantly between platforms, and Steam's larger user base typically drives substantially higher sales.