If a bias is a point of view, then everyone with a point of view on something is biased. The question is contradictory.
In a court of law, eyewitnesses offer stronger testimony than non-eyewitnesses. Therefore, the biblical writers offer the best evidence for Jesus. “But they were very biased; they can’t be trusted!” The amount of bias is a consideration but not solely. Should the eyewitness testimony of Jewish holocaust survivors be rejected because they were very biased? Some Nazi’s and Muslim would say yes, but is that not due to their even greater bias? If one is going to reject all bias, if held consistently, they’d have to reject everyone’s testimony, their own testimony, and their own position.