First I was torn apart between Sanji and Big Mom, but in the end it's undoubtedly Sanji.
- Sky Walk, which Sanji learned throughout the time- skip was portrayed as nothing special in the New World.
- Sanji as the only Strawhat, had to share his first fight in the New World with Jinbei
- In his next fight in Punk Hazard, Vergo cracked his leg and Sanji might have implied he would've lot
- Next arc Sanji was lol- diffed by Doflamingo
- in Whole Cake Island he lost to Judge
- He was pummeled his brothers
- Attacked his captain to the best of his ability, without any resistance whatsover
- At the Wedding he was send flying and held down by Daifuku
- In the Seducing Woods he saw Brook and Chopper being in trouble and yet was flying away
- He said he is going to knock out Big Mom, but ultimately failed
- He said he is going to save his captain, but failed
- Was smashed by Yuen
- Saved and outright mocked by his brothers at the end of Whole Cake
- Oda took away the character development Sanji had, by erasing his memorys with Pudding, including the kiss
- Sanji claimed if he will get stronger then not by the science of the Vinsmokes
- Sanji said he'll get rid of Page One in order to decrease the enemy's forces and he even used the suit of his horrendous father, proving Judge partially right, only to P1 being at Onigashima and by that making that plot point absolutely pointless and decreasing Sanji's credibility as character and fighter further
So here we are, 10 years into the time- skip and Sanji still has not a single noteworthy win (unless you count Yonji being of paneled as such), he turned from being Mr Prince to a damsel in misstres, from being a competent fighter to hype tool for other characters for the majority of the time- skip , from being a credible character with flaws to someone with no credibility at all and from being black leg to clown leg due to the Raid Suit. Chapeau Oda.