If Sonic Generations Collection generated the same gross revenue on the Epic Games Store, Devil's Details would keep approximately $25,246,227 - that's $4,331,829 more than on Steam.
At this revenue level, Epic's concrete platform fee would be $3,306,304. 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 $19,986,772.
Note: This is a hypothetical comparison. Actual sales volumes differ significantly between platforms, and Steam's larger user base typically drives substantially higher sales.