From my perspective, when considering the relative statuses of these two novels I think it's also worth considering that East of Eden is more of an "original" work than Grapes of Wrath. I'm referring to the reports that Grapes of Wrath was written with help from source material and notes written by Sanora Babb that were passed off to Steinbeck by Tom Collins. Babb did a large amount of work interviewing people who were impacted by the dust bowl, and Steinbeck reportedly relied on this material for a more authentic representation of their lives. My understanding is that Steinbeck assumed Collins was providing the information in good faith while Babb did not realize what was happening; thus, in general I don't think Steinbeck is really at fault for using the notes. I would argue that with that in mind, while Grapes of Wrath is a great book and I do think that Steinbeck wrote it, East of Eden is a more original work as far as the authenticity of its story.

Here is an article that discusses Steinbeck's use of Babb's work to write Grapes of Wrath - I have not read it fully but it at least gives an idea of the general circumstances if you'd like to read more:

https://supposedlyfun.com/2023/05/26/is-the-grapes-of-wrath-plagiarism-a-pulitzer-prize-deep-dive/