Given that there were much less to learn 100 years ago, was the duration of degrees shorter then than it is now?
In the U.S., the Ph.D. is longer now on average, especially in the sciences because of the influx of money for paid research, the use of grad students to do research, professors as almost pure managers and grant funders versus real working scientists, etc. It has become something like Renaissance painting done by subordinates. Except I still think the painters got their hands dirty and gave instruction.
There is almost no apprenticeship in R1 science from the professor, just other students and perhaps post docs. It is essentially about milking the grad student for results to get more grants, travel, promotions, grow the empire, etc. Thus the expectation for work product has gone up. Add onto that, that the money has enabled way more actual Ph.D.s to exist, but not increased the number of geniuses in the population and fundamental advances are if anything harder as simple much of the low hanging fruit is plucked. And you have a situation of volume of result being emphasized. Not the trainee education.
And enjoy the job market at the end...
All that said, if you sniff around you can find profs or even departments that still emphasize the classic 4 years. But you will have to search. It is abnormal now.
I would argue that on average these degrees take longer now, so yes, they would be shorter back then. Why do I say this? Because today there are many students who might take internships for a year, many students take longer because of more distractions available to them, more institutions exist now, and because supervisors typically have substantially more administrative tasks they are responsible for now suggests that it’s more likely supervisors also have less time now to give to their graduate students then they did 100 years ago.
I don’t know if “there’s so much more to learn now” is as solid as the reasons that I have suggested. Yes, there is more to learn, but it doesn’t mean everything is relevant to learn. We also have tools to significantly boost our productivity in order to manage that intense growth of knowledge (think how much just one computer screen can boost productivity, let alone 2-3 of them).
These reasons, among others, are probably factors that would contribute to longer graduation times.