Depending on a single revenue source is the exact opposite of being independent; which is why they are always that outraged if someone proposes some reduction in funding. They are 100% dependent on parliament will. (...whether this is something you want your media to be, I don't know. It's a very German thing.)

But of course it's not only financially. The German Rundfunkrat is basically designed to be the very essence of what other cultures might dispraise as corporatism. - Despite it's justification as some cross section of society.

I'm not necessarily against the idea but the institutional design of German state media is arguably very bad.