Sanji was designed to be third strongest Vinsmoke son. His name literally has 3 in it, just like Ichiji's name literally has 1 and Niji literally has 2 in it. Oda just now gave Sanji a suit with a 3 on it, 2 on Niji's, 1 on Ichiji's to reinforce that notion.
Anyone thinking that Niji loses his 2nd spot or Ichiji loses his 1st spot is as big a clown as those who claim Sanji > Niji or Sanji > Ichiji