LuckyR- all I know is that I repeatedly beat people far better than me just by resolving to make them hit 90% backhands. People make it more complicated in their heads because they feel more proactive if they are "mixing it up" and might not feel mentally stimulated by doing the same return of serve over and over and over and over.
And books aren't necessarily focused on 4.0 and below tennis where backhands are so much weaker than forehands. And people don't pay for books that are 1 line long.
POUND THE BACKHAND!