The vast majority of historians do not consider history to be a scientific discipline, certainly not in the sense commonly meant today, and are well used to working with a less-than-ideal set of sources for their work. Arguably, this lack is a good thing, in that it encourages more imaginative approaches to the evidence, more sensitive readings of it, and less dogmatic evaluation of a topic, period or place.

In any case, and to address the specifics of your question more directly, historians are typically happy to acknowledge the existence of bias in both sources and secondary accounts of history, and indeed consider this bias potentially very useful and revealing as a subject of study in itself. While there is always more to say, you might like to review a couple of earlier responses that address this problem while you wait for fresh responses to your query: per u/DanKensington,

Here's a secret: History is created by, charted by, written by, and studied by humans. Humans are, by definition, biased. 'Unbiased' history is a myth. It's all biased. All of it. But that is not a bad thing. u/mikedash examines the matter of bias here, and u/Georgy_K_Zhukov does the same here.