I think the vision is that this is something you might do on rare occasions and not the be all end all way of making money in the game (which it currently seems to be for many people).
After just starting rare trading, I did find myself not trading ANYTHING but rares. With such high profits there is NO reason to trade anything else. So I do understand what FDEV is doing. You can't have that kind of trade profits in the game and still think people will trade other thing.
Also, if players keep posting pictures of how many MILLIONS they have in fully loaded type 9s when other player have been living off 400k in Cobras for months, it's will only show FDEV how badly this trade is unbalanced.