i had an argument with some people that if madara and itachi fight, madara will ultimately win. other people think itachi will win. i dont why people make itachi so strong.
the only chance itachi would have is use the legendary genjutsu sword he has.
Due to kishi not mentioning what the limits are of these legendary weapons he has one can say if itachi gets a chance to hit him with the sword then he can potenially beat anyone.
But Logically speaking the legendary weapons must have limits that we dont know other wise what would be the point in trying to get haxxed genjutsu,ninjutsu and taijutsu.
Madara would win ofc, but due to the lack of knowledge of the legendary one could say itachi has a chance. Simular case to itachi,naruto,bee vs nagato.
Nagato owned them all untill itachi used the legendary weapon he has. althoug in that case nagato being paaralysed made him a sitting duck. he canr move.