So, as I understand correctly:

Patreon integration shows a mix of your Creator and Member Patreon accounts

You can't easily change the campaign you are linked to

You have to make a separate game page and can't make an integration for some files on an existing page

I am furious, this is such a raw feature that actually makes no sense. I tried to use it, then I just removed it because it's much easier to just let patrons download files from patreon without any itch involvement

It's for paid projects. So you can give download keys to your patreons without doing it manually.

If you have the same files on the Itch project as would be accessible in your patreon, that feature is redundant, yeah.

On the other hand, what about people that cancel their patreon subscription. If they have claimed a download key, they will still have that download key, I would assume.

There probably are use cases for this, where this integration is helpful. Maybe someone can explain a use case here.