If A Dance of Fire and Ice generated the same gross revenue on the Epic Games Store, 7th Beat Games would keep approximately $10,226,142 - that's $2,112,953 more than on Steam.
At this revenue level, Epic's concrete platform fee would be $1,258,110. 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 $8,038,976.
Note: This is a hypothetical comparison. Actual sales volumes differ significantly between platforms, and Steam's larger user base typically drives substantially higher sales.