[Genei Killua]

I wouldn't make the assumption that Gai's taijutsu is better than Itachi's. We haven't seen much of Itachi's taijutsu,

Spoiler:

but we know it was enough to take down 3 fully developed sharingan users simultaneously in like .2 seconds,

and, in a combination with a counter-attacking genjutsu, was enough to defeat Kurenai in a few seconds.