Here's a proper answer that I've already said before but a bit extended.
The main three all started out as failures to their respective superiors:
Ace & Sabo > Luffy
Kuina > Zoro
Other Vinsmokes > Sanji
All three got beat up by those superiors.
The difference is, Luffy and Zoro then got picked back up by their superiors, laughed it off, and then supported one another. Sanji got laughed at, beat up more, neglected, and then thrown in a cell with even his identity killed; no support.
Later, all three are forced apart and sent to islands to get better and improve.
Luffy and Zoro got mentored by teachers that cared for them. Sanji got preyed on, called a liar and chased with no mentor having to train and discover things himself; no support.
Luffy and Zoro now have fate, and CoC working in favor to power them up, Zoro a special sword and Luffy a god fruit.
And now finally years and years later Sanji has modifications given by his abuser and person who threw him away awaken in him, having been forced on him to begin with against his permission but working to ENHANCE the abilities he had to learn and train himself with as you guessed it; no support.
Why Sanji hasn't awakened CoC yet: Luffy and Zoro had support. Luffy and Zoro weren't told every single day they were worthless, a nobody, and beaten up and neglected for it in their infancy until it got into their head and believed it. Luffy and Zoro didn't have their acting parental role models as a kid tell them the only reason they're alive and locked up is because the neglectful guardian didn't have the heart to kill them. Luffy and Zoro may have had hard childhoods but they weren't put through brainwash and Stockholm syndrome to break them.
Yes a conqueror doesn't usually break .... when they have the will. But when forced to believe it, even a conqueror will give up: Luffy ready to break and give up before Jinbei reminded him what's important. Zoro bowing to his enemy to get better.
Sanji just had it put into him in the ages too young where it imprinted. There was Zeff, but it was far too late to fix the lasting damage. Not to mention mother dying as well, so grief. Then starvation..
Yet child Sanji while broken still did have a will, ran away, didn't give up his dream, didn't give up cooking, lived through impossible odds and only put it all aside for a life debt.
So to call Sanji priveledged when he's had to survive the most, endure the most, fight himself, and work to equal others the most is an insult to the highest degree.