The hosel design is what sets the shaft extension line, so if we use the same head (constant COG) the hosel is the only thing that determines toe hang... You are rotating the club face during your swing, so you are just swinging the putter. There is movement in a few planes and axis. If the shaft extension line is closer to the hosel this means more toe hang because of the in increased moment arm and less toe hang the closer it get to the CoG. I can send you some material if you want to look into it more.
A face balanced putter will have a lower rotational MOI than a toe hang putter. You can just pick up both styles of putter and twist them in your hand. You will be able to tell that the face balanced putter is easier to twist. This I because there is less of a moment arm created between the shaft extention line and the COG of the putter head. Face balanced putters will be easier to release, thus increasing the rate of rotation of the face with same torque applied than will a toe hang putter. It's science not an opinion.