Good point, this is also one of the aspects of skill. There are techniques you can use effectively to mitigate this.

One unfortunate thing is that poorly done, orals can be very uneven.

There already is unconscious bias. You can see the student's name, their penmanship, their writing style, you likely know who they are, etc. An oral exam just changes things by changing the bias to accent, inflection, annunciation, skin tone, dress, etc.

The examiner doesn't even have to use the oral exam to give a grade. They could use that part simply to figure out whether the student passes or fails. It's very difficult to cheat in an oral exam. Combine the oral exam with the written exam and you could get an overview of what the student knows.

I'm not sure about that.

It certainly could, but it also certainly couldn't. I imagine being confidently incorrect is likely to produce a worse result than being unconfidently(?) incorrect, for example.

Similarly, a less confident speaker may end up spending more effort justifying their answers, which could better expose their knowledge.

I think it would depend quite a bit on the examiner in this case. Some people may even be simply biased against particularly confident speakers, particularly considering the relative positions of the speaker and examiner.

It doesn't if the examiner understands the material. You can't bullshit someone who knows much more about a topic than you do - bullshitting with confidence will only make you sound like a fool.

If the examiner isn't much more knowledgeable about a topic than their students, then something else has gone wrong.

Not much if you do it well. Confident and wrong won’t get you far, either ...

The real world also privileges confident speakers.

Schools should be teaching kids to be confident speakers and readers from an early age.