Overall, I would say this was a pretty good arc. We found out that Sanji was taken by Big Mom and his family for a forced marriage. Everyone was talking about how this arc was gonna be Sanji's redemption for his complete uselessness since the time skip. But to me Sanji didn't advance in anyway, he is still the same useless loser that hasn't been able to do anything to benefit the Straw Hats since the time skip. To me there are three main things that stand out about this arc: 1) Jinbe joining the Straw Hats; 2) Brook getting the poneglyph and breaking the picture of Mother Caramel; 3) Luffy beating Dogtooth 1v1 with no help from any Straw Hats or anyone at all. After he beat Doflamingo everyone said he couldn't have done it alone, even when he beat Cracker he had some help from Nami. Now he beat someone stronger than both of them and he did without help from anyone. Proving that while he does value and depend on his crew and friends for help at times, that when it comes to fighting he can still find a way to defeat the strongest of opponents himself, as he has done through out most of the series. To me Jinbe, Brook, and Luffy were the stars of this arc, Sanji was there.