The only ancient point defense weapons are machine guns, ancient pe-primitive prototype lasers, and Phalanx systems. So why would machine guns still be effective but the others wouldn't be?
There are no stats for ancient pre-primitive prototype lasers so I do not mention them, but if they got stats than of course the quirk could be applied in specific usage cases. And Phalanx systems would exactly fit the case of where the combination of ship&machine-gun&quirk that would replicate a ship with a Phalanx.
To aim a mass driver you have to aim the warship or space station. That's just how guns that aren't mounted on a flexible mount would be aimed.
And thus a single line of hexes instead of an firing arc. Many other weapon systems are not as restricted such as from having integrated aim adjustment equipment, a flexible mount, have indirect actuation (like from a waist in case of a 'Mech), or even guidance systems, resulting in a firing arc.