Why would FS be necessary for someone who can slow down time?
Also , If oda wanna give FS to Sanji , he dont put as a story. Just he draw panel that show he has a FS.
My theory is Sanji have already had advanced CoO. But Oda shows over woman-sense. Actually , oda shows if sanji focused to anybody , he can perceive easily no matter what.
Also , i dont know why. Odas strawhat haki ability improvement so slow.
Zoro first time black blade - Dressrosa
Sanji first time coa black hardening - wano
Zoro first time CoC - wano
Just , i cannot solve why oda put slow down thing for sanji ?
To avaoid laser beam shower absolutely needs advanced CoO. With Basic CoO , nobody cannot escape all of them .