You don't send constabulary coast guards vessels to a major exercise whereby they sail with major warships and practice defending against simulated attack by enemy jets. Some level of self-defence capability would be nice.
Have a look at the Singaporean navy, they are starting to equip their patrol vessels (their new Independence class LMV) with Mica VLS system.
I am not proposing turning the OPV into an OCV, but it would be nice to have the OPV to be fitted for some additional capabilities when needed, in the sense of mission modules or in the traditional "fitted for but not with" way.
I don't see anything that the ACPBs are doing anything war like. Yes they are on an exercise but that doesn't mean that they are going to do any combat ops. It's good training for the crews to participate in such exercises because they won't be on ACPBs for their whole career.