Well we don't really agree about the book. I don't think that, in the right hands (director and actor-wise), it plays like a sitcom at all. And I don't think the book is weak or that it hasn't aged well. In this case the book was not the problem, it was the way the casting screws up so much in the book and brings up other questions and holes that weren't there. The issue wasn't the show it was the director and this half-baked poorly thought-through gender-switch version.
I just think that the way it was written was specific to a male Bobby and a male experience, and I think the way they switched genders made everything make abundantly less sense dramatically in pretty much all ways, rendering songs like "Someone Is Waiting" nonsense and "Marry Me a Little" a useless shell of what it once was, now triggered by a scene that has been changed to gut the scene of its actual point and emotional resonance and evolution into the song. Truly baffling how this was allowed or how/why anyone thinks it works or makes emotional sense or structural sense for the show.