Well spotted -I think you are right! It would not suit Sir Thomas self-image at all if he felt himself to be in the same category of persons as the likes of Sir John Middleton, Mrs Jennings and Mrs Bennett.

Of course he goes about putting his scheme for Fanny into effect more quietly, but if you think about what he actually does, there really isn't a lot to choose between his machinations regarding Fanny, and Mrs Bennet's in relation to Jane and Lizzie. Packing Fanny off to Portsmouth hoping she will be so miserable that she accepts Henry as the lesser of two evils is pretty low IMO, even if Fanny is keen to see her family again. At Least Sir John Middleton only embarasses Elinor and Marianne by teasing them but does not otherwise interfere.