Zhou Tian's Abyss Angels, having occupied those territories, must surely station some personnel there. Otherwise, if Zhou Tian's Abyss Angels capture a castle and immediately retreat, although it would still achieve Zhou Tian's goals, the territories would soon be reclaimed by the Modified Angels.
Clearly, if those castles had no effect at all for the Abyss Angels, they wouldn't have carried out such an action and forcefully occupied that territory.
For Zhou Tian, achieving the planned effect requires defeating the Modified Angels, which is possible. However, given the Modified Angels' condition, defeating them is no easier than outright annexing Paradise. Under the current circumstances, for Zhou Tian's Abyss Angels to achieve their goal, a hard fight against the Modified Angels is not a good choice.
