If Hell Let Loose generated the same gross revenue on the Epic Games Store, Expression Games would keep approximately $135,515,196 - that's $15,428,654 more than on Steam.
At this revenue level, Epic's concrete platform fee would be $18,342,981. 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 $107,700,724.
Note: This is a hypothetical comparison. Actual sales volumes differ significantly between platforms, and Steam's larger user base typically drives substantially higher sales.