I thought that's what you meant. The counterargument is that having the shim bridge across the stem slot protects the steerer from the sharp edges of the slot, which are in an unnecessarily stiff section of the hoop due to the screw bosses, whereas the shim is uniformly flexible around its whole circumference so the shim slot is unlikely to do any harm wherever else you put it.
I thought that's what you meant. The counterargument is that having the shim bridge across the stem slot protects the steerer from the sharp edges of the slot, which are in an unnecessarily stiff section of the hoop due to the screw bosses, whereas the shim is uniformly flexible around its whole circumference so the shim slot is unlikely to do any harm wherever else you put it.