Just a thought in order to bring Cunning and Spirit up to the level of Physique. Or it could count for just one of them if only one is not powerful enough. The numbers will definitely need to be tweaked; please just let us know what you think of the concept:
Spirit now provides 1 to all magical resistances per 100 points, and 1 to all maximum magical resistances per 1000 points.
Cunning now provides 1 to all physical resistances per 100 points, and 1 to all maximum physical resistances per 1000 points.
Theory
I feel like this is such a low value that it wouldn’t take too much away from Physique, especially since resistances are capped. However, if you really want to invest into Spirit/Cunning, you could get +1% maximum phys/magic resistances, or maybe even +2% if you specced heavily for it.
Most builds by end game will be aiming for 50%+ on most resistances, if not 60-70%+, meaning that every extra point of resistances is worth that much more. So in this way, it would definitely not be useless to sink some points into Spirit/Cunning.