As far as I know the DoF for the 1.2 m43 is f2.4 in FF world thus f1.8 is shallower and therefore spread wider. I think the number of aperture blades play role too.
I am seeing the picture with 42.5/1.2 is sharper even at this small size
magnification. You are magnifying x2 as a result of using a cropped capture. Compare at the same magnification (meaning look at full frame at 50% and 4/3 at 100%) and you'll see them the same (with same lens on both cameras).