https://pijul.org/faq.html#did-you-solve-the-exponential-mer... answers it, at least partially. There may be a more comprehensive comparison, though.
Where Darcs has this:
https://en.wikibooks.org/wiki/Understanding_Darcs/Patch_theo...
Pijul has some text saying "we're better than Darcs in these areas".
https://pijul.org/faq.html#did-you-solve-the-exponential-mer... answers it, at least partially. There may be a more comprehensive comparison, though.