Alright, let's go through these one by one.
He didn't let anyone down because he still helped his friends free Robin. It was a difference of opinion. Usopp and Luffy sorted that out like pirates and Luffy agreed after that that Usopp left. Sanji never had Luffy's approval. Sanji even gave him to Big Mom's army.
A short fight that should calm tempers. Vivi then trusted Luffy.
I even almost agree. But I'm sure Chopper would have gone after him. Luffy didn't have to do much to convince him.
There has rarely been anything comparable before. No wonder Robin didn't trust Luffy. They messed with the entire World Government. That's why Sanji should have known better. After everything they went through together, didn't he think there was a way out?
Luffy wasn't his captain back then, but his enemy. After that, they formed an alliance and became friends.
Brook only knew him for a minute. Sanji had known Luffy for over two years. He knows what they have achieved in Alabasta, Sky Island, Enies Lobby, Thriller Bark, Fishmen Island and Dress Rosa. Brook didn't know anything about Luffy. Can you see the difference?
Sorry, I don't know which plan you mean right now. Jinbe was the man with the plan. He calmed Luffy and convinced him to be smart. Why did Sanji hit Luffy? Because he didn't believe in him and wanted him to fuck off the island forever.
Yamato knows that both are important. She said herself that she waited a long time for Luffy to arrive. Didn't she think Luffy would rise again and keep fighting Kaido? And Momonosuke is the future shogun.
I like Sanji too, but that wasn't a character depth, that was a disappointment that damaged his character a lot - at least for me. He promised to return, he couldn't keep the promise. He insulted and beat up his captain instead of at least saying why he couldn't go. He didn't trust him. But he instead trusted Big Mom, who said she would let Luffy and the others go. At the same time that Brook was fighting Big Mom (!) and Luffy was ready to rip his arms off for Sanji, Sanji wanted to bring some food to Pudding to finally satisfy his perverted needs.
Sorry,
@soheilhazrat, I didn't want your thread to go in that direction, but I needed to clarify. Nami is still great!