f-droid isn't strictly better. It isn't really an alternative as a store for a ton of apps, as it will only accept open source apps as a matter of policy. Which is certainly their prerogative and might be good enough for some people.
But I use some apps that are non-free and are perfectly fine with those apps being non-free and want to use these apps anyway. So f-droid will never be a full replacement for me.
The real benefit of the F-Droid ecosystem is that it's easy to host your own repository. And the client is explicitly designed to have multiple package sources avialable, so the developers of these proprietary apps can easily host their own repo.
Afaik there's no readily available payment system. It's not impossible to build one and integrate it with F-Droid though I think.
But I use some apps that are non-free and are perfectly fine with those apps being non-free and want to use these apps anyway. So f-droid will never be a full replacement for me.