That was obviously because the Gokage et al didn't know exactly who Tobi was and any intel on him was low. Because most of the Shinobi world didn't know who Tobi was then, most things were on his terms. So for him not to fear anyone at that point, was expected. And coming back to the topic, in which we were hypothetically speaking, Tobi would be afraid if the whole shinobi world had full intel on him, knowing who exactly he was and what he stood for.
PS: This scan is also another proof, clearly showing Tobi's reaction towards someone who had intel on him(he was shocked). [
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I don't know where you derived that reasoning from. The whole statement implies that Tobi was referring to intel. Although it is a little vague, you could easily argue that Tobi was afraid of Itachi's observant mannerism and his ability in finding out the truth about him. The fact that he is actually Obito. This would allow Itachi to find ways to either capture or kill Obito, even if it meant allying with Naruto and other Konoha shinobi to do it. This is what Tobi had feared. He feared Itachi because of this. Not necessarily because Itachi was more adept than him in fighting. Also, I'm certain that Itachi himself too mentioned "how Tobi was the only one he couldn't kill" or somewhere around those lines. I'm too lazy to find the manga scan but it was definitely during his confrontation with Sasuke. Most likely the final fight between Sasuke and Itachi. :hmm: