Again and again, its not the same thing. What that does isnt create a prefab it makes a BP (class) which has ChildActorComponents of that type, its similar to a prefab but it has all the bells and whistles of BP which might not be actually required by a simple prefabricated group of Actors.
That it is but you have to work around the limitations of the current system and those limitations are arbitrarily imposed by the way the current (kinda like) prefabs systems functions 
I think the keyword here is simple, not everyone needs access to the full Blueprint graph, construction script, child actor templates etc they just want a quick easy group of Actors they saved previously and can place in the level as instances.