ok, i see a lot of ppl assuming since A>B than B>C which is stupid AF lol, as no one possess the same exact abilites, nor the same fighting style that isnt a logical argument at all.
Nagato may be pushing it, but the others remain fair game IDGAF lol
Everyone is focused on Itachi and mentioning the Sasuke vs. Deiadara fight, but that has nothing to do with this, until you're considering the abilities displayed in that fight and how they would relate to Itachi vs. Deidara.
Now, as a member to Deidara created two strategies against Itachi, his scope (for genjutsu) and C4 (probably for susano). As we no it'll work on regular genjutsu, it is known how it'll fair against tskuyomi, IMO it's fair to exclude that. Now, this leaves amaterasu which could easily catch Deidara, but one must consider their fighting style, not the way you would handle the situation. Itachi always goes for genjutsu and Deidara takes flight, as this starts the fight, genjutsu would be countered (and since Deiadara doesnt have sharingan, Itachi would most likely use a regular one. Nonetheless, I excluded this). After Itachi acknowldged his failed attempt and notices Deidara move to fly, he'll use amaterasu (logical move). However, Deidara's birds are big enough to block Deidara himself for taking the hit. Now, this really only leaves susano and C4 (unless I forgot something).
IMO this is not a situation in Deidara's favor, as this is how both parties fight and have displayed this on a number of occasions.
