Makes me wonder if that is all the munitions they have to throw, or if they calculated it would be more than enough for the one ship.
They likely thought that the odds of more than one ship was next to zero, so it was an all or nothing thing. Being unsure as to the EDF ship's capabilities, they would have to give it their all to overwhelm its likely defenses. And any ACVs that survived could be recalled, just in case, but would be out of the fight for the moment.
I really like the design of the station, are they based off the O'Neill cylinder concept?