Very nice analysis. And I agree with most everything you wrote.

However, I have always read Marianne's statement to Elinor as a deliberate barb - the kind only siblings know how to give. She hits her where it hurts. I have never believed that Marianne actually believed that Elinor really thought this. (wow that sounds complicated!)

"But I thought it was right, Elinor," said Marianne, "to be guided wholly by the opinion of other people. I thought our judgments were given us merely to be subservient to those of our neighbours. This has always been your doctrine, I am sure."

Marianne is arguing with her sister here and Elinor calmly responds.