That last one is a real problem-solving strategy, I can't tell you exactly how to balance a Red-Black tree but I know what a Red-Black tree is and where to look up the algorithm for balancing it and I think that's good enough.
One of the master skills for interviewing is "don't choke." Often good people will make mistakes under the pressure of interviewing and will drop out.
When it comes to a practical session there is the same issue that some good people will choke. Just the sample of who chokes in which environment when is different.
Issues like this turn up in all cases where people try to measure merit. For instance, it is known that some low-SES (socioeconomic status) people will choke on standardized tests like the SAT or IQ tests. It is also known that some high-SES people are as dumb as posts and will have that revealed by standardized tests which are harder to bribe or bullshit.
The hostility towards testing is explained by the combination of those two groups: primarily the Emperor doesn't want you to see they have no clothes, but people have sympathy for poor people.