The Corellian/B-wing was essentially flying junk, typically only used by cash-strapped pirates, built using wreckage found at various battle-sites.
The Ugly's mission profile usually only required the vessel to damage lightly shielded targets. Against heavier-shielded and better-armed vessels, the Ugly was less than a match. The cobbled-together nature of their construction also meant that very few Uglies could be relied upon to perform at anywhere near peak levels.
Later "refinements" to the design included an anti-infantry turbolaser, intended for use on the ground, attached to the ship's undercarriage.