If Assetto Corsa Competizione generated the same gross revenue on the Epic Games Store, Kunos Simulazioni would keep approximately $32,667,781 - that's $5,428,195 more than on Steam.
At this revenue level, Epic's concrete platform fee would be $4,318,334. 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 $25,890,280.
Note: This is a hypothetical comparison. Actual sales volumes differ significantly between platforms, and Steam's larger user base typically drives substantially higher sales.