There's the problem, you guys don't use rational thinking. Deidara's mobility rules out Totsuka Blade (as far as we know, it doesn't have unlimited range), Itachi's long range three tomoe looking attack (Itachi admitted he, naruto, and bee didn't need to "aim" their attacks when they destroyed Nagato's Chibaku Tensei), Genjutsu (he'd be too far away to make/have to make eye contact), I'll give you Amaterasu, but Deidara can also prepare multiple mobile bombs while Itachi is preparing Amaterasu; moreover, Deidara can avoid Amaterasu through clay clone, he can also fuse with his large clay creatures. Susano'o counters most of Deidara's bombs, but I'm not giving it c4, or c0 (I shouldn't have to explain them) Susano'o MIGHT be able to withstand c3 (which is still stretching it). I'm not denying Itachi's skill, he's extremely powerful, but using logic, Deidara CAN solo Itachi. I'd even be willing to Rp anyone's Itachi to prove it. p.s. Itachi hasn't been shown using Izanagi so don't say that, and Izanami wouldn't work on Deidara (He acknowledges what he's capable of, and Itachi's Genjutsu prowess (he wen't so far as to train his eye)). I could add more, but I think you get the point.