So the trade route yields have changed quite a bit since the patch. Mostly for the better, I think is the consensus. What isn't quite so clear is how it all works out. I've played a game where it's seems quite rare to get a decent yeild where you're not giving the opposition two or even three times what you're getting which seems a complete reversal of what was going on prior. In any case it has led to this rather strange situation in a new game I've started where I can make an external trade route for absolutely nothing. That is, there is absolutely no benefit to either party, zero, nada, zilch. I can't tell if this is following the adjusted TR logic or should be considered a bug. It's certainly counter intuitive!