Sanjis initial reaction was:
1. Save the Straw Hats
2. Take one of Big Moms pirates hostage
3. Tell judge and big mom to shove it.
The only reason he accepted his role in the wedding was realizing that there was no other way to save everyone.
When Gin put a gun to Zeffs head Sanji didn’t back down, he stopped fighting back and told Gin to point his gun at Sanji instead because Sanji was protecting Zeff and his dream with his life. Or is Zoro willing to sacrifice himself to Kuma for Luffy him “backing down” from his dream?
And you’re using the Kalifla and Black Maria incidents saying Sanji backed down? Sanji merely showing that his principals are things he’s willing to die for is a conqueror trait. Conquerors don’t back down on their beliefs as you said, and clearly Sanji will never bow down on his principles there
All of the examples you gave was Sanji either standing up for those he lives, or for the beliefs he hold most dear to him. All of which are constantly shown in conquerors.
Sanji only did that because at that time he still thought he could be in control. He still gave up and lost the will to fight after he over heard Pudding telling Reiju his whole family is to be killed at the wedding and had to be knocked to his senses by Luffy. He couldn't find and muster the strength by himself.
Zoro only backed down after he tried and failed to knock out Kuma with Death Lion Song, his last attack while everybody else was down. When Sanji gave up to Gin, the rest of the cooks from Baratie were still standing. Luffy was still fighting Don Krieg.
And its not CoC users not backing down on their beliefs, its not backing down against
impossible odds. Ace never backed down when he fought whitebeard alone or was losing to blackbeard, Hancock never backed down even at the Navy's threat of rescinding her Warlord status, Kidd never backed down even though he faced impossible odds against Kaido and Shanks.
Sanji meanwhile: asks why Zoro dosen't give up to Mihawk, gives up after Gin threatens Zeff's life, gives up against Kalifa in water Seven, gives up against Big Mom and Vinsmoke Judge in WCI, gives up against Black Maria in Wano.