If Horizon Zero Dawn™ Complete Edition generated the same gross revenue on the Epic Games Store, Guerrilla would keep approximately $107,121,469 - that's $12,847,406 more than on Steam.
At this revenue level, Epic's concrete platform fee would be $14,471,109. 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 $85,114,805.
Note: This is a hypothetical comparison. Actual sales volumes differ significantly between platforms, and Steam's larger user base typically drives substantially higher sales.