The reward of the PhD can be measured in different ways, depending on the reason why the degree is used.
E.g do you use it to get a good job or position? In certain cases, if you apply for a post and the application mentions that PhD will be considered, it will probably be more valuable, compared to other qualifications. Not always though...
It’s certainly not easy to quantify the value of a doctoral degree or any qualification generally. If it's done though, it will probably rely on certain objective factors, such as time, publications, which can be measured easily.
Alexander Ohnemus in my opinion, i think the value and reward system in academia, including the emphasis on the time spent in school, can vary across disciplines, institutions, and even individual academic advisors. If the awarding or recognition system of a particular institutions is rooted into the direction of time spent in school, then i guess the value of the research is being downgraded to that effect.
Likely because of the self-patronizing view of administrators who produce precious little scholarship and hire or support people who validate the administrator's minimal scholarship (e.g. Dr. Claudine Gay, President of Harvard, has produced 13 professional papers and one dissertation).