> I just mean that if you put 2 experienced people talking about a topic they both know, it should be pretty easy for both (or at least the interviewer) to get a rough understanding of the level of the interviewee.

Well, in my experience it's not, at least not in a "hostile" context. Most technical people are used to assuming good faith in technical conversations, and there are some very smooth bullshitters around; it's easy to construct a verbal facade that only falls apart once you ask someone to actually code.

Anyone who can't see through the 'verbal facade' is not that good. They may be very smart, but not at a bonafide genius level.

It's not. You will find plenty of examples in this very thread.