Author Austen's society is set up to lubricate the social friction in ways that ours is not, but, from reading her works, it is clear that she thinks the point of propriety and breeding is that of easing the comfort of those around you. Not every good heart in her books believes this, but the ones that evince manners without a heart do not have her approval.
Mrs. Jennings shows her generosity by wanting good for all the people in her life, however she misinterprets how that should be accomplished. Sir John tries to impart happiness and comfort for the majority of the story (although he seems to miss that many of his choices of jokes, etc., cause discomfort. Lady Middleton is too well-bred to be impolite, but it is implied to be a kind of self-pride in herself, rather than ever being the result of compassion or sentiment.
Mrs. Palmer shows a kind of selfishness even before she tries to take Mrs. Jennings with her away from Cleveland, in that she does nothing to make Mr. Palmer more easy in company, nor does she understand something as simple as Elinor not wanting to be reminded of Willoughby's injury to her sister all day every day. Mr. Palmer's compassion can be awoken, it seems, but most of what we see of him is himself wrapped up in himself. Nancy and Lucy Steele are obviously pretending to have good qualities that one doubts in them. Willoughby (and Sophia Grey?) may understand such compassion, but do not allow it to rule them when selfish considerations are in contention.
Naturally, the best characters are the ones we are supposed to like best: Mrs. Dashwood, Elinor and Marianne, chief among them, with Marianne becoming what we want her to become by the end. Is this how it is in real life: the pleasantest people are the ones who overlay a warm outlook with good manners?