The idea of wanting barges that are reasonably capable of PvP and also reasonably good at mining simultaneously just sounds like wanting to have your cake and eat it too. Ships should be specialized.
Miners would probably adapt by never mining with any other ship. PvPers would adapt by just bringing something that can counter your navy barges. We call this power creep.
Mining barges have already been buffed extensively, perhaps even excessively, with regards to survivability in PvP encounters. If they need to protect their fleets they already have many options like cloaky Falcon alts, hidden battle skiffs, citadel weapons, etc. There’s a thousand ways a mining fleet can bait and destroy any would-be pirates.