Before the DNA molecule was observed or had any predictive or explanatory power, anyone could have said that there is no evidence for it if it was simply proposed. However, the notion of a molecule was observed and existed before DNA. Hence, the proposal wouldn’t be too radical.
Compare this to postulating the existence of a “living” being made of light such as an angel. Clearly, there is no evidence of this. But one might say there was no evidence of a DNA molecule before it was observed. But clearly, the angel postulation seems “more” evidence-less given the fact that we’ve never observed a “non physical” being in any way, shape, or form, much less if that concept is even coherent. What is the best way to differentiate theories that each seem to have no evidence?