The point is: Vergo landed a clean hit on Sanji. Which is why he broke his leg. The fact that Sanji tried to block the attack is irrelevant in that matter.
That’s like saying someone attacks you and you use your shield to block but your shield cracks and your arm is slightly injured. Had the shield not been there the attacks full force would have been set.
Sanji blocked the attack but suffered minor damage. Why else he not try to block again after realising how tough vergos body was? Hence why he dodged the second kick and didn’t choose to block it like the first. If Sanji didn’t block that kick and instead took it to the face instead then I would call it a clean hit where the intended amount of damage was done. Sanji was sending Vergo into walls and causing him to bleed where as the only injury Sanji suffered was a crack from a blocked attack. Deny it all you want it’s there in the manga in black and white and you can read it whenever you want