Trade posts for feudal rulers are kinda OP.
The situation for them is even worse as it was in Res publica: they give you a ton of wealth, and because there is no redistribution, it is effectively just a massive boost to income.
If you manage to "conquer" TP, it gets kinda ridiculus: there is a hard cap for the number of TP you can have, but if you manage to accumulate more than the limit, there is no event to put you back to the limit.
Example: Playing as the king of France (started with Louis the Stammerer), I inherit 2 TP: Paris and Sarcelles. After some time, I declare a "Carolingian reconquest" on the Carolingian Empire (WTF?! I don't think it should be possible) for Provence. I win, and lo and behold, I now own the TP of Provence!
I am at 3/2 TP, no malus, TP of Provence has ~35 BT, castle in Paris ~20 BT.
I make 20 gold/month, and I'm like "this is too easy".