While Ghost Rings may be more accurate when firing slugs at distant targets, the accuracy of a bead sight is enough and speed is more important at home defense distances.
Well, it's a start.
Please explain why you think GRS are slower than a bead.
Also please mention if you have ever:
Owned a shotgun with GRS
Fired a shotgun with GRS
Handled a shotgun with GRS
Can you explain the difference between GRS and a peep sight?