Itachi, People grossly underestimate how unbalanced genjutsu is..there is a reason ninjas was told to run in a 1v1 against an uchiha..there's a reason why instead of just kai method, ninjas attempt to counter their genjutsu wholly (lack of eye contact)
getting caught in a genjutsu, even a weak one, can be detrimental in a fight... in the time it takes for a ninja to realize he's in a genjutsu THEN use kai to break that genjutsu....The ninja who casted it could easily run up and cut their head of in a few seconds...
People will say, zomg, you think a hokage will just fall to a genjutsu..... Orochimaru prime hokage candidate #1 ...
Raikage A to Madara...
Deidara....
Kakashi...
etc..