Niji is faster than Sanji. Fucking Big Mom gets tagged by a lightning bolt
He's Dengeki blue and produces lightning effects when he kicks people and that's it.
Literally nothing about how fast he actually is has been stated. The man has a something called "light speed sword" and that's still not indicator of his actual speed.
Also Enraged big mom isn't counted when making stats. She's massively faster than even base Luffy when we see her try so the whole Zues lightning thing isn't a feat. She didn't try to dodge so we can't say she actually can't react if she tried