Raikage can not move at the speed of light. And Haku can only move at light speed in between her her ice mirrors/switching positions, which is only in a very limited small space. It’s not the same. And questioning the validity of the statement means you are putting your own personal opinion above what Kishimoto wrote. I don’t get why this is even a thing ..
I don’t know anything about negatio, but whatever it is, it has nothing to do with the scan.
It's nice to see no one mentioned the basic ninjutsu Itachi knows and the fact that he can form a strategy during a fight.
Now, I don't know much about Grimmjow, so I may seem biased. However, taking mindsets into account and other factors as well, it should be close fight with either side having a chance to win.
Sure, Itachi has his genjutsu and Susanoo, but that's not the only thing he has. There's a lot of outcomes, but only 3 will come to mind and that's if someone knows about the characters fighting.
The way I see it, is if Itachi can actually find Grimmjow's weakness, if he even has any. And Grimmjow has to watch for both genjutsu and kamikaze shadow clones, that actually buy Itachi time to formulate a plan.
The character with the higher stats or better hax, isn't always gonna win the fight in the end. But anyway, I'm gonna call it a draw on my end, as the majority of the scenarios all end with both characters countering each other, resulting in a draw.