I think the question is rather they are equivalent. For example, let's suppose someone does a quick PhD in 3 years, no masters, then all things being equal, t

I think the question is rather they are equivalent. For example, let's suppose someone does a quick PhD in 3 years, no masters, then all things being equal, they are likely to have less breadth than someone who took say 6 years (including masters). Exceptions abound. A rather difficult study might be to see how many postdocs a person with a 3 year PhD does compared to one with a longer PhD, or survivorship, but teasing out other factors would be a nightmare.