If The House of Da Vinci generated the same gross revenue on the Epic Games Store, Blue Brain Games would keep approximately $3,069,891 - that's $723,387 more than on Steam.
At this revenue level, Epic's concrete platform fee would be $282,258. 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 $2,346,504.
Note: This is a hypothetical comparison. Actual sales volumes differ significantly between platforms, and Steam's larger user base typically drives substantially higher sales.