That is essentially what taking a large cut on your app platform is: rent seeking. It's your ecosystem, but it comes out of my pocket as the consumer (unless you're large enough to avoid, like Fortnite).
Discovery, ratings, etc., and managing payments are services with value, especially for small players with apps that don't have an established fan base before they are released for the paltform. Charging for these services is reasonable.
Allowing people to get apps that don't need these services elsewhere is also a good idea.
