If Borderlands: The Pre-Sequel generated the same gross revenue on the Epic Games Store, 2K Australia, Gearbox Software, Aspyr (Linux) would keep approximately $35,539,521 - that's $5,852,429 more than on Steam.
At this revenue level, Epic's concrete platform fee would be $4,709,935. 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 $28,174,619.
Note: This is a hypothetical comparison. Actual sales volumes differ significantly between platforms, and Steam's larger user base typically drives substantially higher sales.