If Rocksmith 2014 Edition REMASTERED LEARN & PLAY generated the same gross revenue on the Epic Games Store, Ubisoft - San Francisco, Ubisoft - Osaka would keep approximately $5,652,647 - that's $1,251,678 more than on Steam.
At this revenue level, Epic's concrete platform fee would be $634,452. 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 $4,400,969.
Note: This is a hypothetical comparison. Actual sales volumes differ significantly between platforms, and Steam's larger user base typically drives substantially higher sales.