drop one piece if you believe Sanji's backstory holds a candle to Kuma.
Im talking about who suffered the most by the way, the other aspects its all on taste
Although.. It looks like Kuma to be the main target and victim of all the attrocities and evil stuff the One Piece world has to offer, but the CDs are evil for being evil, its a caricature basically. Theres nothing good to expect of it based on what we already knew about Kuma even before the latest chapters
With Sanji the feeling is different, those who should be the people he cares about the most are the worst thing to ever happen to him, had to see the only person who showed him some affection, die slowly for the sole reason of trying to stop his biological father's madness, his existence was supposed to be doomed and still might be in trouble to a certain point, his genes awakened and he still can't explain why he can turn back to normal (not even Oda lol he mentioned it in an SBS and told the audience to pay attention on Sanji)
And as i said i see quite the "parallels" in their background stories... It has been told that their existences are wrong, Sanji for being a human who cares about others, and does "servant work" such as feeding people who are hungry and caring about servants being treated like disposable stuff, and Kuma for being from a race who commited a "crime" against the world according to the Gorosei (Nika is probably a Buccaneer as well which makes it even more interesting).
But for me the most obvious thing is the fact they both had to go through transformations that are supposed to take away their humanity and make them mere tools (as Sanji's siblings are to Judge and Germa, and as Kuma is to the WG). But at the same time they showed they can fight against it, Sanji asked Zoro to do his best and simply kill him cold blooded at the slightest unusual behaviour, crazy when u think about it.. As i said before Sanji's arc is still being written but Kuma's is most likely reaching its end (probably somewhat of a happy ending, given the context he already is inserted which we all know its standards are rough)