I don't think anyone is saying that Brooke Shields or Jennifer Hope Wills are unprepared or that people are trying to come up with excuses for them. But actors who are put in to a show that is already running get far less rehearsal time as compared to when a production is opening from scratch. Musicals tend to rehearse anywhere from four to eight weeks before starting previews. By comparison, Shields and Wills probably got two weeks of rehearsal and one put-in rehearsal. It's just natural that they might take some time to really feel situated in their roles...regardless of what an audience is paying.
And meanwhile, by posting the Talking Broadway rather positive critique of their performance, I was just trying to point out that while you didn't enjoy what you saw, Renee, someone else did.
"Gif me the cobra jool!"