I have to take a closer look on that area. Most likely it is way too small for the bigger settlement buildings, which would cause some weird glitches (and if I make it too big, it will probably look weird in the mountain.
Also I just asked myself, where you got that information from:
nearly every fortress map has at least one Settlement of Outpost building within its walls
As far as I remember, most of the fortresses neither have a settlement, nor an outpost:
Aldburg
Lonely mountain
Edoras
Caras Galadhon
Cair Andros
Cirith Ungol
Dol Guldur
Isengard (both versions)
Dol Amroth
Fornost
Minas Morgul
Minas Tirith
Only Amon Sul has settlements and Helm's deep&Fornost has an outpost inside the castle.
So I would like to disagree with your statement here
But your point with Angmar is correct. All fortresses could get the same treatment as Horde maps, as Angmar really needs to level up its buildings. That's something we overlooked in the past.
Also we could give the campfire a similar treatment as the buildings in Isengard(cursed) - if you are Gondor, you get control over it and you can get troups that way.