Good advice, but it's not that OP has 'zero confidence' in the product. He/she says how it failed the most important test.
>... in my understanding we've failed at the most important thing: finding product/market fit
>... in my understanding we've failed at the most important thing: finding product/market fit
They built something, sure, but the technical cofounder believes it has very little/no utility. That's telling.
Per his OP, the technical founder has not explicitly stated whether he believes that the product has zero utility. Rather he's saying that he found out (from data I suppose) that there is no product market fit for it.
Splitting hairs IMHO.