You dont need a new ship class, you just need transport weapons to be at the same military-grade level as every other weapon.
Lawful and unlawfuls are balanced for combat against each other. Fighters, bombers, freighters, gunboats and caps are balanced for combat against each other. Transport guns and transport ships are not balanced for combat against any of the others, or rather they are balanced for 90% lose against most of the others.
Now we have rules that say, all these ships can fight each other no restriction, and consequences for losing a fight are the same among them, but we're still going to make a specific class lose by design. And in order to accomodate that, we're going to get another rule, called the reasonable demand, to replace the other rules.
Just let the transports fight and we can have "space is dangerous" without any of this crap. Either that or put the ships in different combat arenas with different engagement rules again. Pick one
If two ships meet, the winner should get ALL the belongings of the loser, keep them or sell them or walk away, whatever. But in order for that to work, the ships need to have even footing. This game insists on tying down one class, then trying to limit the amount of damage after the fact. Give the transports equal equipment and you wont need to do any babysitting.