If Divinity: Original Sin 2 - Definitive Edition generated the same gross revenue on the Epic Games Store, Larian Studios would keep approximately $120,234,563 - that's $14,039,506 more than on Steam.
At this revenue level, Epic's concrete platform fee would be $16,259,259. 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 $95,545,675.
Note: This is a hypothetical comparison. Actual sales volumes differ significantly between platforms, and Steam's larger user base typically drives substantially higher sales.