Eddie Campbell has described Alan Moore's scripts for From Hell
as being 100-page long essays on subjects many and varied -- and not necessarily about the Whitechapel murders. Campbell then had to distill from Moore's ramblings something to draw.
Based on several readings of Moore's "Twilight of the Superheroes" proposal for DC, I imagine the From Hell
scripts looked similar.
For the record, I am not holding up Moore's scripting style as something to emulate. As with all things, Moore is clearly an edge case.