A trader should never, ever fight a combat build. It's called a trade ship for a reason, it is meant to haul lots of goods from A to B, not to engage in dogfights. Even the Clipper gets a lot more sluggish if you fill it with cargo, now imagine something with the turn rate of a T7. Why would anyone ever engage a ship in those craft?
Multiroles, yes, they could stay and duke it out, but again, they sacrificed combat ability for internal components, so of course they will turn tail and run when the going gets rough. If they are hauling, they won't just lose their ship, they might also lose cargo worth the rebuy cost and more. Traders are built for running goods, and running away when outmatched. Well at least in theory, because the T series couldn't even outrun an imperial fighter without exploding, if it wasn't for SCBs. And that is my honest opinion.
As for the alpha damage.. yes, I personally don't PvP, but the meta seems to be geared towards high alpha damage, be it ramming, torpedos or whatever, to negate the power of SCBs, or drawn out matches. That is why I said that I wouldn't mind some more drawbacks for the SCB, but to completely remove or annihilate it would be a mistake. Traders can and should use it for protection, and large vessels have no other alternatives, given how horrendous shield recharge is.
EDIT: Seeing how efficient the NPCs are with beam lasers lately, you could also do beam lasers + heatsink instead of railguns and PA. But honestly, there's only 5-6 types of weapons in the whole game, and the kinetics suck at shield breaking. So you either use Rail, PA or lasers. That's about it. Not really much of a build diversity, now is there.