There is a big difference between fitting man-portable and/or crew-served weapons on something, and fitting a multi-tonne gun or missile mounting to a ship, and then doing everything required in order for it to actually function. There is little sense in trying to fit a gun onto a ship, if the vessel were to likely be damaged by firing said gun. Similarly, if launching missiles would likely damage or even mission-kill a vessel, then desperately trying to add such armaments on would be doing no one any good. And yes, hot gas exhaust from a launching missile could damage/disable radar and/or comms arrays.
To reasonably address such issues, the Arafura-class itself would have needed to be FFBNW as part of the design, as well as including damage control features more commonly found in warships. Otherwise the discussion about adding on armaments would be sort of like discussing adding box missile launchers to merchantmen to provide an air-defence capability...
Indeed, but I am quite sure you’ll recall even the Arafura in it’s down-graded spec from it’s sister class Darussalam Class OPV‘s were designed for and intended to carry a larger and more powerful main deck gun than the “interim” (cough…) gun they are carrying now, so in part that issue is already covered off in some regard. I’d also not be surprised at all if the Arafura’s were capable in a design sense of operating the 57mm Mk.3 as fitted to her sister ships. We know cost was a driver of the class not capability and we know that RAN did not design out medium helicopter capability from the pad and superstructure of the ship. Such design changes afterall would have incurred substantial engineering changes (including cost and schedule creep) to the base platform.
As Vol will attest it’s the system that primarily effect cost, not the steel, but wholesale changes to literally design out medium helicopters or a gun as capable as a 57mm Mk.3 would have been extensive AND expensive (and quite unnecessary).
Which is not to say any improved combat capability is planned or even required at present, but ruling it out completely is a bit silly given historical precedent.
As to missile blast concerns, there is no doubt engineering studies would be required, even to add modular systems, cold-launch or otherwise.
But it’s a bold statement saying it “can‘t or won’t be done. Afterall, we know anecdotally that RAN has investigated options in this space and we know historically RAN has a long history of up-arming it’s ships during their service.