That is not true. It depends on the situation and the judge.
It is becoming more and more common for dashcam recordings to be admitted.
I am very happy with mine.

I had a very good experience abroad when I was involved in an accident. Thanks to the recording, I got off as not guilty, and since then I've always had one installed in my car.
But in Switzerland, too, it's probably good to know exactly how an accident happened. I don't think any judge will find me innocent if he has seen the recordings. Fortunately, I have no experience in this regard.

A city police officer in ZH had pointed out to me that in case of doubt (i.e. testimony against testimony), a dashcam might actually be taken into account.

Thank you very much! I guess I don't need it then, as I would have only used it for proof purposes.

To be able" - or not to be able - to serve as evidence. That is the question for the judge. For me, the good conscience simply goes along with the fact that I could have proof if something were to happen...