If Factorio generated the same gross revenue on the Epic Games Store, Wube Software LTD. would keep approximately $141,902,272 - that's $16,009,297 more than on Steam.
At this revenue level, Epic's concrete platform fee would be $19,213,946. 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 $112,781,352.
Note: This is a hypothetical comparison. Actual sales volumes differ significantly between platforms, and Steam's larger user base typically drives substantially higher sales.