I think the several storylines are in the hopes of having viewers get hooked on these "new" but also familiar characters (new in the sense they hadn't been the focus, like Violet and Francesca, the other Featheringtons, the Mondriches and even to a point Cressida), while they're still watching a show that looks very similar to how it started, only Daphne and the Duke have really departed. Because I expect season 4 will have very little or no Penelope, Anthony, Kate, and perhaps even Colin. So the cast will be shrinking in a way, and it's best to get us invested in these other characters now.
Of course some also make sense in terms of the books. Francesca does get married early on, because her book takes place once she's already been married for a bit. I don't find her dull, I think she has social anxiety and would love to see that well represented.
Also, there's the fact that this season had to do less to establish the characters because they're characters we already knew. S1 introduced us to everyone, S2 to the Sharmas. But the main couple here was established, we knew them and therefore there's less screen time for establishing their personalities and goals and problems.
My very lengthy two cents.
the actress who plays Francesca is beautiful.
I haven't read the books, so I don't know if he's a scoundrel or not yet, but she deserves someone who notices her as she is without having to play games to get suitors attention
Francesca just seems super boring so far, albeit ever so pretty. Eloise is, as she always was, a bit of a rude cow. 
wish they'd released all the episodes in one go though - annoying to have to wait for second half!!
