Jesus some people can’t distinguish between reader knowledge and character knowledge.
The fucking point of it was that the readers knew it was a Robin situation but Sanji made the straw hats think it was an Usopp situation which is why Nami acted that way because as you said they dealt with it before it was one member selfishly leaving the crew and fighting the captain. The only people who knew differently was Sanji and Luffy which is why Luffy knew that each kick Sanji threw hurt Sanji just as much as it hurt Luffy.
what a load of bull, the whole point of all that was that Sanji didn't believe Luffy and the crew could help protect Zeff or beat Linlin, her family and crew, that's why he gave up running away and accepted his fate of marrying into the BMP, Luffy coming and trying to bring him back made him waver and doubt what he should do, that's why his meeting with Pudding calmed him down and he was sett on marrying her until he heard what Pudding said about him and what the BMP were planning, at that time he had no choice but to run back to Luffy and ask for his help.