If Backpack Hero generated the same gross revenue on the Epic Games Store, Jaspel would keep approximately $3,643,379 - that's $840,691 more than on Steam.
At this revenue level, Epic's concrete platform fee would be $360,461. 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 $2,802,688.
Note: This is a hypothetical comparison. Actual sales volumes differ significantly between platforms, and Steam's larger user base typically drives substantially higher sales.