American oratorion is generally awful. Talent in it command a premium. Perhaps this is related to our lack of oral examination ? We’re more comfortable with written argument because that’s how we’re taught to think?
But, in general, oral communication is harder than written. Written form allows you to take time to form sentences, correct mistakes, reorder thoughts, follow an outline... Oral communication, on the other hand, forces you to think and speak in parallel. It's always going to be harder.
In my opinion such examinations and written finals succeed in filtering out people who can only regurgitate what they have been spoon fed in class rather than being able to use that information to move forward. I think I was lucky to study when and where I did, it stood me in good stead in industry.
Of course there are some people who really do find such examinations difficult. In my opinion the solution is to provide assistance to those people to do better rather than throw the baby out with the bath water.
- Pressure to actually talk and perform. In a written exam I can stop, look at the paper and take my time to actually start. In an oral exam I have the professor looking at me. Less time to actually think.
- It's harder to communicate orally with complex subjects than in written form. Add to that the extra cognitive load of not dealing with your native tongue.
- Time constraints on oral exams punish students that don't learn everything by memory but can reason in real-time. I didn't know by heart a certain proof, I know for sure I could have done it in a written exam with time to spare (it wouldn't have been the first time) but I wasn't quick enough for an oral one.
- Mental blocks are much harder in oral exams. Some times I blank out and forget something basic (e.g., the derivative of a logarithm). In a written exam I can stop, think, and solve it. In an oral exam, the "stopping" is already making you look like you don't know things, adding pressure that will make you underperform.
Written exams have been the norm for decades for a reason. Far easier to actually ask the things you want, they scale far more easily, easier to correct and grade, and easier for students to practice and perform well.