I keep repeating this: two things Steam does right are effortless no-questions-asked refunds, localized prices in many regions of the world, so that people in poorer countries pay affordable prices. I do think that Steam is only going to grow bigger, because most of the growth in game sales are going to come from China, Russia, India, Indonesia, Bangladesh, Africa, Mexico, Brazil etc than US and Europe. But most othe…
Personally I'm being conservative, that the Epic Store will lack of a lot of features upfront and need a higher advertising budget, and some additional support costs if I have to self-administer cloud saves (eg. via AWS) if Epic don't have that feature yet.
So I've budgeted for about 10% lower sales, 50% increased advertising spend, about $10k extra development costs. I come out slightly less profitable than Steam, but I calculate that the risks of launching on Epic are much lower, since there's a chance that the game can just flop and die immediately on Steam on launch, whereas at least on Epic I have the boost from being selected. Plus, the potential upside on Epic is much higher.