If Grand Theft Auto: San Andreas – The Definitive Edition generated the same gross revenue on the Epic Games Store, Rockstar Games would keep approximately $9,619,599 - that's $2,023,350 more than on Steam.
At this revenue level, Epic's concrete platform fee would be $1,175,400. 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 $7,556,499.
Note: This is a hypothetical comparison. Actual sales volumes differ significantly between platforms, and Steam's larger user base typically drives substantially higher sales.