You do realize both Parade and Bridges had book writers, right? Not just book writers... extreme heavy hitter playwright book writers. And especially on Parade... "he" didn't decide to do most of it, it was a collaborations with an older and very respected and awarded writer, Alfred Uhry, who had already won a Tony, a Pulitzer and an Oscar for writing who had a personal connection to the time/place/story/issue, and Hal Prince the biggest and most awarded director Broadway has or will ever see... and it was JRB's first book musical. And for Bridges he worked with a giant of directing again, and Marsha Norman who had already won a Pulitzer and a Tony for her book to Secret Garden and had written several other musicals including Color Purple.
My point is he did not create the story, structure, or characters for either musical. If anyone "trotted" out characters it was the book writers, and with no objection by the directors.
I'm not sure i agree "Another Life" is the *best* song in Bridges... it is a great song, but it is one of many.