Re: Sasuke, more powerful than Itachi.
Zetsu stated that Itachi's performance was so that he wouldn't be surprised if Itachi was severely injured before the fight even started. He didn't dodge or dodge properly attacks that he should have been able to avoid with ease, and he coughed up blood and collapsed when he used too much power, both of which Zetsu considers highly unusual and attributes to his possible condition. According to Zetsu "That definitely wasn't Itachi's true power", and not only was it noted that his movements were completey different but that he even looked different. In addition, although we know that his overuse of the Sharingan had taken its toll on him, while Zetsu's dark half suggests this as the origin of the problem, his light half says that's not it - but he couldn't quite put his finger on it.
I'm pretty sure Itachi could've handled Sasuke in better condition. The only thing shown here is that Curse Seal Level 2 Sasuke might have better ninjutsu power. As for genjutsu, all that was shown was that Sasuke was more capable, as far as technical efficiency and that, with a weaker weapon, not that he had better genjutsu plain and simple. For example, it was good enough to counter the Tsukuyomi, being a weapon of similar function, with his skill, however he could never produce anything on that level. But it was enough to get away, and make genjutsu pointless. When they had fought through illusion earlier, neither seemed able to fool the other, so I'd say they're actually pretty similar in this area - Sasuke's skill making up for the raw difference in the power of the illusion, Itachi's power making up for the difference in how it is handled.
Also, it might (or might not) be something to note that both mental/spiritual energies and physical energies are utilized equally in the formation of chakra for jutsu creation. This could perhaps give significance to Itachi's condition as related to his ninjutsu power.
It's not like the Mangekyo Sharingan isn't part of Itachi's power, so I don't know why you exclude that anyway.
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