If Company of Heroes 2 generated the same gross revenue on the Epic Games Store, Relic Entertainment would keep approximately $34,912,560 - that's $5,759,810 more than on Steam.
At this revenue level, Epic's concrete platform fee would be $4,624,440. 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 $27,675,900.
Note: This is a hypothetical comparison. Actual sales volumes differ significantly between platforms, and Steam's larger user base typically drives substantially higher sales.