oh my... I really don't think Sanji is stronger than Law by just using Vergo as measurement.
Firstable Sanji got Vergo by surprise. Vergo never went at him at full power. Sanji made no harm to Vergo, neither did Law.
Vergo was after Law and also we can assume that he used much more power to tackle him than Sanji.
There are too much uncertainties to make any notations on whose who by looking at past fights. But as a supernova Law is considered to be closer to Luffy than Sanji what comes to fighting. And of course physical attacks can be seen as Laws weakness. Vergo is Law's cryptonite, super fast and physical, who also knows all Law's tricks and abilities.
Sanji however is also physical like Vergo, but Vergo beated him in Sanji's own game. That means Sanji got pretty much owned as well. Vergo is at the moment best kicker on the island... well if Luffy's axe or spear doesn't count as one.
