>Talking through a few whiteboard problems and talking about tools they have used (why and how) are sufficient.

I've done interviews with a whiteboarding "tell me about stuff you've worked on" component followed by a test.

It thought it gave a weak signal about the skills of the candidate. I canned it eventually because the test gave a very strong signal and it wasn't telling me anything the test didn't.

>Interviews with higher management is just a redundant filter and another reason for the management to justify their existence.

I agree. I had suspicions in a previous company that this upper management "team fit" interview was adding a race/nationality filter that ended up with good candidates getting dropped.