The high wing aircraft will be more stable laterally than a low wing. When an aircraft is banked it starts to sideslip. If you just look at the sideways component of motion, in line with the banked wing, the drag line of the high wing aircraft will be above the centre of gravity and so the drag produced will tend to roll the aircraft level. You get a similar effect from a high T-tail.
So, leaving wing sweep out of this, high wing aircraft (C172) doing the same job as a low wing aircraft (PA28) need to have less dihedral.