I've just rewatched some of the 1st series and like others have said, it feels a lot more realistic. In episode 2, Jenny helps a young pregnant prostitute called Mary; her story is in the book and it's absolutely harrowing. A couple of the conversations Jenny has with a priest who also helps out are very different from the "Nonnatus House saves the day, we're so knowledgeable about everything" storylines in the recent series.
First, the priest comments to Jenny that it must all be a shock to her and she breezily says she works in the East End and knows about poverty. The priest replies "I don't think you do nurse. Poverty isn't just about poor housing and a lack of food, it's never having been loved or even respected." Jenny then acknowledges that she is naive.
Later on, she shouts at the priest after seeing the awful state Mary is in after her baby has been taken from her. He shouts back that she isn't the only one who's angry. But with a baby, no family and no education, how can Mary support herself other than by returning to prostitution. It's a case of which child do they save - Mary or her baby - and sadly there are no happy endings.
If they included her story now, you'd get Dr Smug mansplaining that prostitution isn't great, telling the world-weary priest he's wrong and then finding Mary a convenient job by the sea where she can live in with her baby.