User blog comment:Techterror/What do you want about ships and components?/@comment-204.126.146.202-20180821232305/@comment-26159325-20180830230834

Now I wouldn't say that they are absolutely useless as I have a suspicion that their purpose is not to make your base do significant damage to attacking fleets but instead serves to make your base much more difficult to destroy, enabling any defending fleets to deal more damage before the station falls. However, as I don't think anyone knows the formula that determines the interaction between armour and attacking power, we cannot say that it is completely useless at this moment.

However, the view that most people hold is that there are far better things to spend your building slots on other than any Defence Module (such as resource buildings or shipyards).