I did do a German search as well. And bias in that case would be something like "parteiisch" "bevor-/nachteilen". In 2019 a court did say it gives an advantage to incumbents because you had to limit your results to 8 parties. They've changed that since. The article you've linked is talking about its usefulness in general and not that it gives unfair advantages to anyone.

Honestly, I'm not a big fan of the thing myself and I agree that most of your proposals would improve the tool. But calling it a tool that compares political parties biased makes it sound deceptive. And I don't believe that it's deceptive. It's just ineffective.

The fact that it gives an "unfair advantage to incumbents" also isn't really a bias of the tool. It really just is the most obvious fair way to structure it. Large parties are large because a large amount of people vote for them. So they obviously have more visibility.

But I also agree that the majority rule of an ageing population in Germany is problematic. With most incumbents seemingly agreeing to not talk about the future.