Well, if you compare 20 y old Minato to 20 y old Itachi, Itachi clearly has more feats. Now I'm not saying Minato<Itachi, cause we have simply seen too little about Minato to justify that. But he did become hokage in a young age, so he must have been capable of more, than what we have been shown.
Nonetheless sadly we can't conclude on unproved feats, thus Itachi>Minato by manga facts, given that he has full knowledge, but who hasn't heard of the flying thunder god technique? Well everyone knows it. U_U
Now I see you are talking more about talent. Let me remind you hat Itachi became ANBU Captain before he gained MS. Itachi didn't have MS long, besides Itachi has stronger and more advanced jutsu than Minato. It may be true that Itachi didn't invent much of it himself, however, Tsukuyomi obviously is his invention.
If you understand that left eye ability of his (which Sasuke also has in the right eye), you would know that the strength of tsukuyomi, doesn't come with the MS like something free. Same goes for amaterasu and Susanoo. All 3 are very complex jutsu, and you need extreme skill to master it perfectly. We have no knowledge, how long it took Itachi to master it, however, Sasuke had just a short amount of weeks. So Itachi probably needed same, though his tsukuyomi is way stronger.