Backlog milestone to my understanding is because on trac you couldn't have no milestone assigned. So no milestone and backlog are defacto the same. Personally I prefer no milestone to backlog, tho looks a bit awkward if there are only a few with no milestone. Anyway I treat them the same.
This is where I think Delenda Est has an advantage, in that the capture mechanic is clearly defined and localized.
With capture out of the picture for the vast majority of buildings, you can do things like adding HP to Fortresses, adding special techs that increase that HP further, add more crush resistance, etc.
Capture bar limits these possibilities, leaving you with balancing the balance of previously balanced capture system.