That's not particularly true. I don't think there is a single mathematician whose papers are understandable to laypeople (by laypeople, I mean the average person, who remembers some but not all of highschool math). What's really going on here is that Einstein made a tremendous contribution to a tower that was already quite tall, while Darwin's contribution was to the ground floor where everybody could get on. The maths analogy to Darwin would be one of the inventors of Algebra - evolution is taught to children right along with the foundations of math and physics.
Also one of the selling points of relativity in the early days was the difficulty of its math. I think it was Eddington who said that "only three people understood General Relativity."
I see your point, but if Darwin created a new field but Einstein contributed to an existing field, Darwin ought to be considered a greater genius. (Personally, I think it is better not to define anyone as a genius so that we can continue to evaluate their work critically.)
I'm saying that we value things we don't understand more than things we do understand.
I suspect that the media would indeed portray most mathematicians as geniuses, though. In fact most laypeople I know would agree that they were, and I know some fairly well educated laypeople in my opinion.
By mathematician, I mean a publishing academic with a PhD in math (or some rough equivalent to that).
Of course he dashed off another three articles in the same edition of Annalen der Physik, all on the same level of comprehensibility, one of which scored him a Nobel prize.
The difficulty of relativity was and is a silly meme. The basic principles are straightforward. I understood them as a boy, and I am - by a regrettably enormous stretch - no genius.
What marks them both is their willingness to abandon the established dogma when it didn't match the facts, and to set off exploring alternative ideas. Both of them are iconoclasts: Einstein because he proposed time wasn't absolute, which is a seriously batty suggestion to just about everyone unfamiliar with his work because we are very familiar with how time works here on earth. To me Darwin the more impressive in this regard because his idea wasn't just seriously batty (no one had seen evolution at work when he proposed it, despite living in it's midst) but just putting it out there was enough to get others burned at the stake.
Another similarity is neither was your typical extroverted iconoclast. Quite the reverse in fact: they doggedly followed their favoured theories because the felt they did a better job of explaining the facts. Both seemingly didn't care that others would think less of them for their ideas.
You can point to others in the same mould: Galileo for instance. The doctor that endured years of ridicule from his peers for suggest gastric ulcers were the result of a bacterial infection is another.
Nonetheless Einstein stands out for second reason: he did it more than once.
Einstein’s iconoclastic idea was his questioning of Newton’s occult force. That was Einstein’s starting point. He could not accept that an occult notion acting instantaneously at a distance can exist in nature. He set out to fix this situation by trying to explain gravity without the Newtonian force. Did he succeed in this?
Also when we look back, we see that Einstein was chosen as a product to be marketed as genius to unite the post-war Europe. A German Jew whose theories proved by the observations of a British team etc.
I think the idea of evolution was in the air. Lamarck and Wallace wrote about similar things. I don’t know if Darwin knew about them.
The book is of course GR bible Gravitation by MTW.
https://www.amazon.com/Gravitation-Charles-W-Misner/dp/07167...
May I suggest that, the media tends to declare someone a genius if his work cannot be understood by laymen. Physicists like Einstein are declared true geniuses because the mathematics they use look mysterious and magical. But anyone can understand Darwin's prose. Personally, I think they are all human and by defining them as genius we deify them.