Best judgement in partial world
Researchers have also claimed that teachers underestimate the intelligence of fat girls and short boys. So should we do away with teacher assessment and base all pupil judgements on external tests? That would hardly be wise given that many tests have also been accused of gender and cultural bias.
The sensible thing to do is continue to have a judicious mix of external tests and teacher assessment. Teachers may not be models of impartiality (who is?) but many are better judges of their pupils than any test.