The AI is quite focused on cargo of any type and if you are flying a transport ship, you must be ready to run immediately. You have to keep an eye on the messages when you jump into a system, that is a prime point of interception. The way to break off that NPC is as soon as you get that "tasty cargo" transmission, jump to another system. I usually drop down to normal space, program my destination, wait till the NPC drops down, hit the FSD to spin up and boost away at the same time. You will lose them. Do not boost to escape unless you have the dirty drive mod (for speed) and shield/armor/shield booster mods (protection), if you do, you can outrun them until they fade out of scanner range. then you can spin the FSD and continue to you destination.
Avoid the escape "mini game" at all costs, all it does is cost you a slow FSD spin up. The instant you get interdicted, cut your throttle to zero, submit. This gives you a quick FSD spin up, boost while you program a new system jump and then jump. You will escape.
Some months ago I quit using any transports, they were too disadvantaged. I got tired of being the mouse so I saved the CR's and bought a Python, slowly a-classed it and haven't looked back. I started to look forward to interdictions back then. The Engineer's upgrade took me back a few steps, became the mouse again, but the Python could still run. I have slowly modded it, FSD, dirty drive, armor, shields, power plant, power distributor, MC's and most recently HD shield boosters. Now I'm able to dictate terms of engagement, run if I want or fight.
I do not carry cargo unless it is for a mission and now have jettisoned all the materials that I had obtained for the Engineers and only carry the ones I need for the mod I am working on. This adds more grind but when(?) they give cargo storage it will resolve the problem.
I recently lost the Python in a poorly managed encounter at an outpost but learned another lesson. Since then, I made the 9 mill CR loss back plus another 30 mill. I have started to go back into conflict zones and HIRES to bounty up and been successful. Also have gained 20% (@82% from deadly to combat Elite).
I am an old guy (62 and counting), so my reaction times ain't what they used to be. If I can do it anyone can.
Cargo carrying is seriously disadvantaged so change your game during the time FD figures out how to rebalance.