It seems the road to CoC and CoC coating is different to each character. I always assumed that Haki to be a regid power system where you advance from lvl to lvl through experience and power lvl, this is partially true for CoA, but for CoO and especially CoC every character has his own hurdles and personality flaws to overcome to advance, case in point Zoro needed to consciously project his sense of self into his sword to advance his CoC while Sanji needed to expand his love inward to advance his CoC.
While Luffy, with his simple character, he didn't face major hurdles to advance his CoC and Haki in general.
In conclusion CoC in particular seems to be a character driven power system. The better you become at understanding your inner self the stronger and more skilled you become.
Haki is Will.
Aisa from Skypiea is a good example. Small girl, no offensive prowess. But, incredibly kind, thinks about everyone and refuses to accept the racism present in her tribe. So, because her Will is to help/understand different people, and she is very brave, she has amazing CoO.
Sanji's always been willing to die if necessary, while Zoro constantly faces death but refuses to give in due to Kuina.
If Brook's Awakening is as strong as I think it is, there's a chance Sanji will actually get to say hi to Sora, and receive her love again.
I think Sora's illness stemming from her saving Sanji's emotions is REALLY the biggest issue here. It's not Judge, his brothers, or even Iva.
Sanji hates himself because deep down he blames himself for Sora's death, when Judge is the one who led her to doom.