So, here’s my question: to what degree did David Mack’s outline for the Destiny trilogy impact upon the writing of Christopher Bennett and Peter David?
I can't speak for PAD, but I wasn't even invited to write Greater Than the Sum until just after Dave completed his outline for Destiny. I was sent that outline as well as the manuscripts for the three preceding TNG novels, and was given the task of creating a story that bridged the gap between them.