If Saints Row IV: Re-Elected generated the same gross revenue on the Epic Games Store, Deep Silver Volition would keep approximately $32,579,356 - that's $5,415,132 more than on Steam.
At this revenue level, Epic's concrete platform fee would be $4,306,276. 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 $25,819,943.
Note: This is a hypothetical comparison. Actual sales volumes differ significantly between platforms, and Steam's larger user base typically drives substantially higher sales.