Itachi, Minato, Jiraiya, Orochimaru, and Nagato are all depicted as Top Tier Ninja with great plot importance from the author and all have the hax'd abilities to back it up, with Senjutsu, Mangekyo Sharingan, Rinnegan, and Flying Thunder God.
They are all within the same tier and it all comes down to circumstance (Knoweldge and Plot). With knowledge Jiraiya could beat Nagato, but without it he looses. Itachi and Jiraiya who have some knowledge on each other but not full could go ether way as he states. Minato wants to fight Jiraiya because it would also be an interesting battle since both have a great deal of knowledge on each other. Jiraiya and Orochimaru both have a large amount of knowledge on each other, but not complete so the match could go ether way which is why they are rivals. Itachi has greater knowledge of Orochimaru's skills than Orochimaru does on him which is why he beats Orochimaru.
I don't think one can say these shinobi stand no chance against each other if circumstances are manipulated.