sassafras
...
- MBTI
- .
I think 'depth' might refer to the relationship between what it's possible to say about a subject vs what is actually said, like it's a kind of property of volume.
This can't work if that 'volume' is 'detail', though, but has to be a measure of 'profundity', which is indefinable.
So basically, a judgment on someone's level of depth would be entirely dependent on how thoroughly you, the Vice President and Secretary of Deep Club, have examined the subject yourself and the novelty of perspectives introduced in conversation.