Why armed cargo ships do not replace dedicated warships

If Star Wars cargo ships can be heavily armed, why build dedicated warships?

Purpose-built warships integrate combat functions more efficiently; most armed transports remain compromises unless conversion was anticipated in their original design.

Efficiency is the answer to why dedicated Star Wars warships remain useful. The small turtleback transports discussed here have limited point-defense weapons and are not intended for frontline combat. X-wings, A-wings, and Y-wings can be attached as parasite craft, but those additions remain separate from the transport's basic role. Mon Calamari ships are treated as a different case because their builders anticipated combat modification. A participant immediately qualifies how explicit that intention was, so their example does not establish that any ordinary cargo hull converts just as easily.