Many actresses prefer lack-luster leading men since that brings more focus on the her character. Bette Davis didn't make so many films with George Brett because no one else was available.
As for Bonita Granville: Big fan. I'll have to seek out those Nancy Drew films since I haven't seen one in a long time.
Before Hitler's Children some of my favorite, non-Nancy-Drew films with Bonita are:
It's Love I'm After - Leslie Howard, Bette Davis and Olivia DeHavilland.
Merrily We Live - Constance Bennett and Brian Aherne.
Third Finger, Left Hand - Myrna Loy and Melvin Douglas.
Escape - Norma Shearer and Robert Taylor
H.M. Pulham, Esq - Robert Young and Hedy Lamarr
The Glass Key - Alan Ladd and Veronica Lake (Bonita is all grown up in this one)
And of course the Davis film Now Voyager.