I suggest making a Defend your land bonus similar to the Orb of power bonus, but only applicable in your borderlands, and is lowered by holding the orbs of power. Gives the defenders of their homeland an advantage, also negates the orb of power bonus to your enemy in your own lands. Then the orb bonus really only makes a difference in the eternal battleground.
Also I think that each borderland should have a fixed number of NPC’s for each world in it and they should be spead out evenly to the control points. It doesn’t make sense that soldiers spawn instantly when you take something but won’t help defend your garrison.