I think you’re misunderstanding what the claim here is. The payments are not necessary for Flathub and flatpak (though they take a cut), it’s revenue for developers. Revenue they would have never seen if their app is packaged in distro repos like normal. Implementing payment systems in the native package format is basically impossible which is why no one ever did it. Flathub is giving app developers (whose job is oftentimes thankless) a chance to receive easier funding or even a livelihood. All around a good thing.