You make a good point, and this sets up the characters for an attraction to the one in the other pair who most closely matches their own personality. However, I do think that Lizzy and Jane interact as equals, because in fact they are - being sisters, and the two oldest in the family - not to mention that they seem to be the most respected in general, also. It's different with Darcy and Bingley - they are both wealthy, but they are friends, not brothers, and Darcy is "old money", while Bingley is "new money".