I think it's important to examine Fanny's comment from the context of what precedes it. Fanny has been expressing her resentment that Mrs. Dashwood will be taking some of the china, plate and linen with her, when she leaves Norland. These are items which had been purchased by Henry Dashwood for Stanhill, the Dashwoods' home prior to moving to Norland to keep house for Henry's uncle. It bothers Fanny very much that Henry Dashwood should leave these things to his widow instead of passing them to his son.

The loss of the breakfast set, in particular, upsets Fanny:

"Yes; and the set of breakfast china is twice as handsome as what belongs to this house. A great deal too handsome, in my opinion, for any place they can ever afford to live in. But, however, so it is. Your father thought only of them. And I must say this: that you owe no particular gratitude to him, nor attention to his wishes, for we very well know that if he could, he would have left almost everything in the world to them" (ch. 2).

In ch. 5, we are reminded of Fanny's feelings about the furnishings that will go with Mrs. Dashwood and her daughters:

It chiefly consisted of household linen, plate, china, and books, with an handsome pianoforte of Marianne's. Mrs. John Dashwood saw the packages depart with a sigh; she could not help feeling it hard that as Mrs. Dashwood's income would be so trifling in comparison with their own, she should have any handsome article of furniture.

I think we must be careful not to interpret too literally Fanny's comments about Mr. Dashwood's feelings. She is bitter over the loss of the plate, china and linen. This must be taken into consideration. Perhaps Fanny saw Mr. Dashwood's leaving the breakfast set and other items to his widow as an indication that he thought only of his second wife and his children from that union. But just because Fanny says it, does it make it so? John is inheriting all of Norland, along with the rest of his mother's money, plus he and Fanny already have their own household and a good fortune on which to live. So Mr. Dashwood doesn't need to be concerned about John's financial welfare. His widow and daughters are the ones who need his benevolence now (which is why, in the first place, he asks John to help them out).