It is stubbornness, and it doesn't make any difference on what they believe and the amount of effort they are willing to put, even dying if it's necessary, and Sanji showed that many times during the series. Luffy was about to give up on everything after Ace's death, he needed Jinbei to remember what was the most important for him. Sanji just didn't realized back then that he also has ambitions and willpower that makes himself put his life on the line if he has to, the AllBlue for example was one of the main reasons of why he joined the crew, where did the idea of "a CoC user needs to respect another" came from? This is something totally linked to a character itself, why would Sanji watch someone he barely met just get killed right in front of him by facing an opponent that he clearly had no chances of winning?
Katakuri's whole path to get CoC and fighting is to protect his family above all things, and he even blames himself for the harm his siblings may get, he just took some time to realize this.
After watching Luffy, Zeff says he relates a lot to Sanji, it's like Sanji was "hiding" something he could see on Luffy. You dont have to live as a stupid to have CoC, you can use your brain too, it doesn't changes who the characters actually is, you just need to step up.
Here is a example of Rayleigh "belittling" Roger, both end up being CoC users lol. You're acting like a CoC user is a CoC user cuz he respects someone elses dream straight away, and not mainly because he has his own character traits, his struggles and personal goals.