The Epic First Run programme allows developers of any size to claim 100% of revenue if they agree to make their game exclusive on the Epic Games Store for six months.
After the six months are up, the game will revert to the standard Epic Games Store revenue split of 88% for the developer and 12% for Epic Games.
I don’t think that’s the same thing as a monopoly. Or at the very least it’s not nearly as bad. The presence of Epic on the market has been great for developers, because they can get good deals at epic AND Valve has been forced to reevaluate their prices.