One of the problems is that trade functions specifically to push value directly to immediately-neighboring nodes, thus enriching them. That value builds with each jump as you then take the stuff from that node and move it forward (plus integrated bonuses). So if you own entire nodes in a nice chain, the amount of income you're knocking around is immense.
At the same time, if you
don't own the majority of the nodes in your chain, you will lose value. A lot of value. Imagine a chain 5 nodes long that you're wanting to move value down. You own 100% of your home / collection node and the adjacent node. You also own the majority of the source node and its adjacent node. However, while you have a couple ports and some ships in that central node in the middle of the chain, you only have 15% of the total trade power (perhaps because many small nations in that node exist and are collecting / moving trade another direction).
This theoretical trade nation will fail to transfer the majority of the trade from that node on to their capital; most of it will instead remain there or forward elsewhere, enriching local nations and competitors. All that work you've put in upstream to create trade value and move those goods across the seas will be magically obliterated in this central node. This is especially bizarre if you have a couple port provinces and some ships there. Where are those goods going? Why are they being straight-up
robbed from you without even having privateers involved? Why can't you just use those ships and provinces to forward on most of that value that you brought in to begin with?
So, with trade, you have to dominate every single node in a chain just to forward the value of goods. If you don't do this you get basically nothing. But once you do pull this off, your income is absolutely ridiculous.
This all-or-none trade game should end. I should be able to colonize West Pacific islands as Portugal, have a few ports dotted around Africa and a fleet of ships, and bring all those West Pacific goods to my homeland. But I shouldn't get the benefit of all those African goods at the same time unless I stop and invest heavily in controlling that region as well (and that should require
more resources). And you shouldn't be required to form massive blobbing empires just to build trade routes!
I made a full thread on this in the suggestion forums a few days ago with some mechanical details on how to resolve this issue. Check it out:
https://forum.paradoxplaza.com/forum/index.php?threads/trade-steering-changes.864216/