OK, let's back up a minute and think here.
1. If above-board, legal trading is unprofitable period, why is it in this game? I mean seriously, this is not just a Newbie Trap, it's just a waste of time and CPU.
2. The fluff doesn't make sense and neither do the tariffs. This is a world where everybody's some flavor of Mercantilist, but nobody's smart enough to form a cartel, let alone let the player sit at the table?
3. It makes even less sense when we're looking at the Pirates and Ludd. Pirates shouldn't have "black markets"; they should probably have port fees at most. I mean, the fluff says they're desperate and the game says their Markets need everything under the sun. They don't make sense.
4. Ludd shouldn't have "black markets" either; maybe a "terrorist tax" might be more appropriate. But historically most terrorists are basically organized criminals with political goals; also historically most terrorists look the other way, in terms of their stated ideals, if they need money for the Cause. It's hard to see why Ludd should behave differently; they aren't the Knights, they're the radicals.
5. Trade routes aren't inherently "boring". "Boring" is when you just circle a huge fleet from point to point, taking hours to do so while your eyes glaze over, and then, after hours of circles, you're rich, because the game mechanics allow that. That's not the fault of tariffs or trade systems; it's that nothing interesting or remotely dangerous happens if you build a big enough trading fleet. This seems like a fixable problem. For example, make your fleet more and more attractive to Pirates based on the value of the cargo you're carrying and the ratio of civilian ships vs. military ships.
To put it another way... Freelancer had totally fixed trade routes. But the Cardamine Run was actually quite fun, because you were practically guaranteed to get jumped by something scary and have to fight your way out.
The problem this game has with making trading (and to an extent, travel in general) interesting is that, once you get past early midgame, practically nobody will try to jump your fleet, period, and anybody who might do so cannot catch you. I've been saying this for years now, lol.