??
Deidara lost to itachi when itachi used tsukyomi on him to join akatsuki, while deidaras was under tsukyomi itachi couldve easily amaterasu'd him to ash.
Sasuke used curse seals, forbidden techniques, a brand new technique that means hes not limited to chakra, and also released orochimaru onto itachi (sannin level) and still sasuke passed out from fatigue, and tobi said itachi was merely playing with him and planned it like that.
Pain could very well beat itachi if he managed to overthrow his yatas mirror, pain would own itachi if itachi didnt use yatas mirror.
Madara maybe, dont know enough about him, but he managed to get away from the 4th without a scratch and the 4th said he saw through all his techniques, so yeah it's plausible madara could own itachi if he overcame yatas mirror.
Itachi's main strength is in yatas mirror, once that has been beaten (IF it can be beaten) he soon admittedly slips down the ranks, but he is still above sannin level and top 3 in akatsuki and top 10 overall even without yatas mirror.