Can Sanji be, in theory, be feared by the Marines?
Let's just say that he has the strength level around 70% of the world's strongest swordsman Zoro.
What other qualities can he offers to instill fear?
- No Poneg reading ala Robin
- No God DF ala Luffy
- No knowledge to build Ancient Weapon like Franky
- Not Ancient Weapon himself like Shirahoshi
* His wife can potentially read Poneg (not big enough threat)
* His status as potential Germa Kingdom future heir (dropped the name)
+ Succesful experiment of human enhancement without drawback: no lost emotion.
So, the only possible, reasonable, and logical scenario he can be feared by the world is if he allows his body to he studied and let everyone in the whole world have the same or similar enhancements as him.
Like some Sanji fans believe, Exoskeleton is discount Mythical Zoan. If this can be amassed, it can be more dangerous than amassing Cyborgs via Kuma (because expensive: 1 PX = 1 Battleship) or Artificial Devil Fruit (because it still has DF weaknesses, whereas Exo didn't).