I agree. Although the Frisco Sour (which is bourbon based) uses lime & lemon.
I think that using Grapefruit in a sour works well with gin cocktails. I've
done a play on a Jasmine:
West Side Cocktail
40ml Bombay Sapphire
10ml Aperol
10ml Cointreau
20ml Grapefruit
Shake, shake, Coupette Cocktail glass, grapefruit twist garnish. Yum.
One thing i would say is no sour mix!