I think it depends on the field, and on factors like quality of advisor, quality of peers, how much teaching you have to do, etc. In CS, for example, people de

I think it depends on the field, and on factors like quality of advisor, quality of peers, how much teaching you have to do, etc. In CS, for example, people definitely come out as experts in some niche of their research. Of course, there's a difference between their expertise and that of an experienced professor, but both are quite far from a normal person's knowledge of the field.