It is not about buying/delivering the app.

It is about doing payment within the app once it is installed. In that case Epic is paying/maintaining its payment infra. Your point is irrelevant

Got it.

So if back in 1999, internet explorer only allowed you to download something, if they took a percentage fee, then you'd be OK this with use of monopolistic power.

Can you think of any reasons why this might not be a realistic choice?