Four characters times seven equipment slots. It's annoying micromangement, and in this case it's especially bad because you are not informed at all where the "red line" is where the amount of Repair needed changes.
Try playing a Rogue and see how fast your dagger degrades in the course of a battle. The answer is REALLY fast - two Durability per attack, and you can get say, an average of three attacks per turn, and that is just for ONE turn in one battle. It can absolutely go from 60/60 to below the red line after a battle.
Yes, and this creates a problem during opening chests/doors with brute force.
It is very realistic, since such brutal use of weapons hurt them, but it should happen a bit slower.
