Managing complexity is a valuable skill that should also be screened for at interview. At most top companies you are there for at least 4-5 hours so there should be plenty of time to evaluate that skill.

I think whiteboard questions are good, I want to know that this person is capable of writing difficult code if we need them to.

I also think we probably ask too many of them.

I have been on the hiring side and my experience so far has been that almost always the feedback is close to identical across multiple whiteboard questions. The questions are also so abstract that asking multiple to "prevent bias" seems ineffectual. What bias could there be, you either solve the problem or you don't. Bias is more likely to come in on the behavioral interviews. There should be multiple of those for sure.

Generally someone is either a good enough coder or not and they will display that consistently across all the interviews. You will see the same stuff throughout (good or bad variable naming, good or bad communication etc) thus asking > 1 coding question by default is a waste of everyone's time.