well when it comes down to these two people to say itaichi can just use Amaterasu or Tsukuyomi then the 4th will be done just means you really underestimate minato and as we dont know the full extent of the 4th and his sealing we cant say to much as the only fights we have seen him do is fight fox and a short fight with tobi so its not much to go on, and the Mangekyō applys strain on itaichi so if he would mess up then minato will have plenty of time to attack, but itaichi isnt dumb id say his intelligence is on the same level as the 4th.