If Trombone Champ generated the same gross revenue on the Epic Games Store, Holy Wow Studios LLC would keep approximately $3,405,948 - that's $792,126 more than on Steam.
At this revenue level, Epic's concrete platform fee would be $328,084. 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 $2,613,822.
Note: This is a hypothetical comparison. Actual sales volumes differ significantly between platforms, and Steam's larger user base typically drives substantially higher sales.