Having state funding as a basis is fantastic and I like that Germany has this as do many other countries. But if the corporate and other donations get top big there will always be a conflict of interest. If you do certain things you’ll get more funding from certain groups. Those who get more funding will have more money to campaign for the election. In gaming this would be called pay to win I guess.
The other issue is that in Germany groups get around donation limits and having to disclose donation sources for larger sum donations by splitting them into smaller chunks and sending them through multiple organisations. That’s why I’d like parties having to disclose every single donation. That’d at least show where their biases might lie.