@desa:
1-Because he decided to block a expert haki user. Logia wouldn't have change a thing.
2-Logia doesn't block a physical attack
3-Sanji fights with martial artists. Not range fighters
4-Well Sanji as done well on avoiding getting shot at Ennias Lobby and fights martial artist so I doubt it will be a problem.
Many people have said already that smokers haki/overall ability was weaker than Vergo's. But here he was still able to not get hit by his attacks(defensively and/orevasively). I think its funny that this was shown after Sanji hurt his leg. This could this be useful for any hand-to-hand fighter? So saying being a Logia and a close fighter is a bad combo can be dismissed. A df ability can be used in many different ways, they can even fit the most specialized fighting techniques. ( http://img.batoto.net/comics/2012/10/14/o/read507b04be72645/img000005.png )
Here( http://onepiece.wikia.com/wiki/Sanji/Abilities_and_Powers )
States:"This unusual martial art seemingly takes some inspiration from the Brazilian martial art, Capoeira, and the Korean martial art, Taekwondo and may have took some from the Chinese art, Tan Tui and bears an almost identical line, in name and in style, to the extremely powerful and dangerous (to both the user and opponent) style, Blood Leg."
I can see how 'his' style can definitely be stressful on the body. This is not me saying Sanji has hit a wall, but I'm just trying there is something to it.
Rob Lucci said, "Regardless of the type of power, it all depends on how you use it. The chances of you weakening from it are very low. Besides, being a hammer isn't much of an inconvenience."
So this fruit can help, screw it, almost any fruit can help. A guy of Sanji's caliber and character can definitely make this fruit useful for the crew.