Same question about "luck" then: should just one or both chars have it?
It is the
average luck that determines drops.
So beefing up the luck of one character is still better than no-one's, but less good than beefing up both's.
I just restarted the game, went for 2 Survivors, focusing on the survival stat and the luck skill, to try it out, with just enough points in Agility to defend themselves and Strength to be able to use the stuff.
Going for Warrior and Mage paths once better spells and 2h / 1h-shield skills become available, with basically only luck from the survivor path.