Just started paging through a book in which the editor quotes another source to claim, "_____ is probably the greatest painter of the last one hundred years." Thirty years after the claim was made, I wonder if the original writer would repeat it, especially since the claim is now 10 years past the era spanned by "the last one hundred years."
It's easier to justify a superlative judgment when applied to personal favorites than to critical assessments. While I believe something extremely rare and precious should be connected to "the greatest" in any domain, I have much less confidence in my own judgment of superlatives as I get older. The impulse to put together lists of superlative subjects is less attractive.
I'm more interested in those things that I return to repeatedly, that draw me to them in a way that I can't resist. My favorite American painters of the last one hundred years would include Edward Hopper, Jasper Johns, Jim Dine, and Philip Guston. Especially Guston. Oh, and Fairfield Porter, Richard Diebenkorn, and Marylyn Dintenfass. (And I regret not to include a host of illustrators, such as Arnold Lobel, Maurice Sendak, and William Steig.)

And my memory fails. And there are so many "greatest" that I have not seen.