I think it's a mistake to think of whiteboard problems as attempting to recreate a real work environment. They are a proxy for the kind of quality you are looking for that can be "measured" within the alotted time.

They can show that the person is prepared (they studied), generally knowledgable (they remember obscure stuff), or just clever (they come up with interesting approaches to the problem).

I'm not surprised you see both excessively simple (make sure they aren't ridiculously unqualified) and excessively obscure problems, since the first one essentially tests your reflexes and the second one tries to determine if you learned your job "by rote"