i think sanji actions were understandable (like when Capone allowed him to leave a note to Straw Hats , I think he should have explained the whole deal with Zeff but I get that considering his personality he didn't want to involve them )
that said the way Oda resolved the issue with Zeff and co feels like a cop-out
Because I'm sorry , but Oda clearly meant for the readers to believe Big Mom herself was threatening Zeff, not just the germa
I have a lot of problems with how Oda wrote the entire Germa Plot and how things don't feel like they fit, but "he should have explained the situation" is ignoring, not only Sanji's predicament, but also how other characters, like Luffy and Judge, would react in that situation.
Let's assume Sanji steps out of the carriage and explains them what's going on.
Judge views pirates as a bunch of scum, etc. He could just have threatened Sanji there, thinking he would be plotting something with Luffy to ruin the marriage. Bye bye, zeff.
If Luffy hears that Sanji is being blackmailed, he probably screams that Judge is a piece of shit and they are going to protect Zeff and fight BM if they have to. Bye bye hands and his cooking, which is pivotal to Sanji, considering his relationship with Sora and Zeff, and his dream of All Blue.
Etc.
You can't write a "drama" scene and just give it a "get out of jail for free" card. That's exactly what happened throughout Onigashima and its multiple fakeouts and we KNOW how shitty those were.
The "sanji hitting and disrespecting luffy" comes from multiple places.
1- Luffy and Sanji's dynamic in Baratie "I refuse your refusal". Luffy is not going to just accept sanji leaving without explaining why, and we know he can't.
2- Usopp vs Luffy duel. The only time Luffy had to "abandon" a member, was when that member defied and disrespected him. Just remember Zoro's speech in water7.
etc.
It's not meant to be pretty, it's not meant for us to go "uhu! go sanji! break those fucker's teeth!". It's meant for us to feel sad that the characters are forced into these positions to begin with, so, when the "turning point" happens later on, it can feel "relieved" that it worked out fine in the end (or didn't work out at all, but that's not Oda's style except in specific situations, like Ace's death).
The entire scene of Luffy not defending himself because he FEELS that Sanji doesn't want to do this and is suffering, how Sanji ignores Nami's pleas, the whole "I know you didn't mean any of this bullshit", the "i'm gonna starve unless i eat your food only!", and "i can't become pirate king without you!". All these moments are meant to leave a bad taste in our mouths. To make us feel sad, angry, desperate, etc, so it can build into a catharsis later on.
There's more to the whole sanji's arc during WCI and the events that follow this "duel", but I'm gonna comment on just this for now.
WCI has A LOT of problems, after all, it's "post-TS One Piece" we are talking about, but the "drama" part I don't think it's one of them at all.