~ Reason why Itachi and Minato should never be compared ~
Itachi's intelligence is dwarfed by the 4th Hokage who was a genius on the level that only comes once in a lifetime. His accomplishments speak for its self, he reverse engineered the Bijudama and created the rasengan, he was the 2nd Kage ever to create a time/space technique through fuinjutsu, Hiraishin was so fast that he could literally kill an opponent in the blink of an eye, and with kushina's help created a jutsu that was capable of summoning the death god.
What has Itachi accomplished? Itachi was really good he sped through the ranks faster than kakashi, and was the greates Uchiha after Madara. Unfortunately the rest of the clan had grown weak over the years. The only reason Itachi is an S-rank-nin is because of the mangekyo and the ability to use it wisely under chakra deficit but it can't be used often since he doesn't have the necessary chakra to use it continuously.
In the end, there is no comparing them. Itachi is powerful but Minato is out of his league.