When a 135 mm gun becomes point defense

Would a twin 135 mm mount work as a point-defense weapon?

It would primarily be a main gun, with a possible point-defence role using fragmentation ammunition against a predictable hypersonic flight path.

A twin 135 mm mount would normally be the ship's main armament. The answer distinguishes that primary purpose from its possible use against an incoming missile. The proposed example is a fragmentation barrier placed in the path of a hypersonic weapon whose ability to turn is constrained. This is a suggested engagement method, without a demonstrated interception described here. The wider argument is that sensor-directed weapons can serve in point defence even when that is not their main role. Crew-served weapons lacking those sensors are explicitly excluded from that generalization.