If Path of Exile 2 generated the same gross revenue on the Epic Games Store, Grinding Gear Games would keep approximately $113,860,316 - that's $13,460,029 more than on Steam.
At this revenue level, Epic's concrete platform fee would be $15,390,043. 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 $90,475,251.
Note: This is a hypothetical comparison. Actual sales volumes differ significantly between platforms, and Steam's larger user base typically drives substantially higher sales.