Most of the time I would expect smugglers to use freighters as it allows more speed and manuverability as well as the ability to hide easier (asteroids work well for that). Transports dont usually make good smuggling ships due to their lack of being able to evade detection. What I saw as a good use for this was a merchants approach / solution to accessing those remote trade routes that are only open to the smaller ships. That would be a good reason for designing a ship that does not offer more then what is already available. If the capacity is going to be capped at 5000 then you need a different reason for making a ship then just getting that extra 500 tons of cargo space. Accessability to previously inaccessable locations would be a major reason to do this. Time is money to a merchant, so a ship that can navigate asteroid fields and enter a tradelane faster would be worth quite a bit to a trader even if it only saves him 5 to 10 min in flight time for the long distance hops.
Correct me if im mistook what I have read so far, the impression I was seeing was this design being a wash because there was no clear reason for its design if the only advantage would be an extra 500 tons of cargo and having to lose all defenses to get it.
