IME, the folks who say this don’t really understand what drives folks to pursue PhDs in the humanities/social sciences…or any subject or the stark differences in the level of study one is able to pursue on one’s own vs as a grad student.
Studying on your own is not the same thing, especially considering you won’t have access to the primary/secondary sources and other research resources you’d have as a graduate student.
And no, access to the public library…even ones as great as ones in NYC aren’t the same thing.
Already, I’ve had to ask grad student/faculty friends to borrow several books from their respective universities which were intro-intermediate undergrad level monographs because the NYC public libraries don’t have them or have lost the only copy in their system for various reasons including withdrawal by the library system due to lack of patron interest*. Forget about the advanced-level undergrad or grad-level stuff. 
- According to librarian friends, most of the reading public aren't as enamored of academic related texts which aren't non-peer reviewed trade books, pop lit, or a minute few 101-level undergrad survey texts which have gained widespread popularity.
And even the last isn’t guaranteed as I’ve found when a younger friend in the NYC area and an uncle who lives in an upper-middle class LA area suburb asked to borrow my survey text on Modern Chinese history by Jonathan Spence because it wasn’t available in their respective local library systems. Surprised considering it was very popular with the reading public for a university textbook.