Having studied both pieces, I'd venture to say the Chopin is the more difficult, but the greatest difficulty of all would be somehow to prove it formally. Perhaps we could do a statistical analysis of a poll of pianists on the subject. Or perhaps, adjudicate (by a large number of judges) the performances of a large number of pianists doing both pieces. I have a hunch we'd find many more who did an at least fairly good job on the Beethoven, but a lousy job on the Chopin, than those who did an at least fairly good job on the Chopin, but a lousy job on the Beethoven.
Well, I know it seems as though I'm being unduly captious not to accept as fact that the Chopin piece is more difficult, but I think that standards of proof as to what constitutes the "difficulty" of a piece have not been developed with sufficient logical rigor. There need to be more objective standards of what constitutes "difficulty". How do we measure "difficulty"? To say that the Chopin piece is more difficult just because examination boards say it is strikes me as being rather arbitrary. I doubt very much if every judge who sits on such a board has exactly the same opinions about the relative difficulties of various pieces as every other one does. Not everyone even agrees that the Chopin piece should go faster. I've seen the Moonlight Sonata at 88 half-notes per minute, versus 80 per minute for the Chopin.