Earlier quoted context omitted.
"monopolize their game's monetization" That is a silly oxymoron. One game doesn't constitute a monopoly; users who don't like it for whatever reason can go play any one of the vast number of games that computing has produced for half a century. What you're saying is like why should Burger King have a "monopoly" on what sauce goes into a Whopper? Gosh, darn it, the market should be open so that you can order a Whopper…
One store doesn't constitute a monopoly either. You can go sell in another store.
Yes. Exactly why the Epic store is not a monopoly. There are alternative stores available. There is no alternative to the App Store on iOS so one cannot go sell in another store.