The embargo cuts Rheinland from Liberty. Liberty is the most populated house, so if you cut the direct way for traders, they will search other routes.
Second, the zoners whale: Most traders are zoners. And as zoners, they shouldnt trade between the houses, but between zoner bases.
Possible solution:
Rheinlanders should allow traders to come from liberty. If Liberty want to enforce the embargo, let them do it. Also liberty should open the embargo for goods, coming from Rheinland.
The traders: Allow 5k transports only for house trading companies. That would force most traders into house corporations.
"Powertraders" mostly want the biggest ship. We are all powertraders, dont forget this. We want to make money in shortest time - inRP, of course. Nerf the whale to 4500 or so, then other trading factions can get fresh blood.