Really interesting comparison between “Eyre” and “Deronda”! Whereas in “Jane Eyre,” as you say, the heroine is able to reconcile her moral principles with other goals and desires, pretty much the opposite is true for Gwendolyn in “Deronda.” She develops stronger and more morally-based values as the story unfolds, but it seems the more moral she gets, the less she is able to fulfill her desires or be comfortable in the world. Nevertheless, Eliot thinks she is still better off: better to be a good person than rich and successful in a worldly sense. Daniel grows more meaningful moral values too, after discovering his true Jewish heritage. And he does get a nice wife and a meaningful life purpose; but he doesn’t get Gwendolyn, who he finds powerfully attractive. As you point out, the form of novel reflects the impossibility of their coming together as the story splits into two plot lines. (Good insight about how form follows theme!) So I think I agree with you: Eliot says “you can’t always get what you want,” at least not if you want to be a good person.
But about Brontë: in the novel, of course, Jane gets it all–morals, social correctness, and all her individual desires. This ending pleases and satisfies many of the readers I have discussed the book with over the years. But not everyone, I have learned, finds this ending satisfying or believable. For one thing, to some people Rochester seems somewhat emasculated at the end; is Jane marrying the same man she fell in love with? For another, her bettered social position depends totally on a melodramatic contrivance. Of all the cottages in all the little towns in England, she collapses on the one doorstep that could open the door to wealth and a higher social class for her? Perhaps Brontë fits her big shaggy discussion of values and far-reaching social critique into a fairy-tale-like narrative, because that is what most readers want. And I do think she argues, like Eliot, for the primacy of morals in life choices. But I’m not sure Brontë herself would say, yes you can get what you want and still be a “good” person. I don’t think, in her own life, that she did.
Would love to hear more opinions here!