As said above, only base skills and characterization is taken into consideration. Kurenai's skill might be equal to Itachi; do not mean that her genjutsu potency is equal to itachi; skill is the aptitude and maturity at which an individual applies his/her forte in the best way or manner possible.
Genjutsu potency is the power of his/her own genjutsu, the skill of the user cannot increase the potency of a jutsu; unless he/she combines it with some other jutsu; like Cee was questioning itachi's skill at amaterasu after seeing Sasuke shape manipulating with his other eye which is not increasing the potency but rather using another resource in combination with the given resource; and in this case, kurenai needs to add any other amplifier in her genjutsu to make it more potent even though her skill is equal to itachi. Itachi can control the entire SA, which is the thought of an experienced elder of konoha such as Shukaku and Ao who saw through perfect jin manipulation illusionary technique; even he can't sense or see through it and it's long range. So unless it's stated or feat-wise shown in the manga, there's no way kurenai can replicate that feat, but that doesn't lower her skill in that particular area.
Edit: Lmao, guys saying ama is sun level and temari is universe level; here's your explanation; temari with some help ripped open the raiton armoured strongest body shield of 3rd raikage which both the bijuudama and FRS didn't do jacksh*t to. So temari can destroy anything in NV considering with some help she can do that much of a damage to such a durable "strongest" guy.
Ama is a yin attack + soul attack (as seen when Sasuke remembered naruto and sakura in his emotions when he casted his first amaterasu; emotions are a by-product of the soul in NV as tobi explained the nunoboku no ken had the emotions and feeling o the Rikudou sage)as seen with it's black colour, it's pretty useful against tailed beasts which are spirits, hence why we saw the Eight tails scrambling in pain while it took a head on molten lava with zero flinching from son goku, another tailed beast. So in that very context, amaterasu is hot as the sun.
And yes, hiruzen indeed is the strongest hokage; it's not just the saying of the data book.
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