Modded it so core-creation costs twice as much. It shouldn't be so incredibly easy to steamroll-annex whole countries then core the entirety in a couple years.
Working on changing unit building so it costs military power to build light/heavy ships. Shouldn't be able to pump out galleons and barques without any care in the world. Since it's not used for anything else it'll keep the AI/me from spamming trade ships to win.
Making idea groups better. As stated a million times, generic national ideas are awful. Seriously. Hell, even Oman's default national idea is better than most others, what with their -50% to naval maintenance.. Was Paradox thinking? How is that anywhere near balanced? Why would someone pick, let's say, Yemen over Oman in that case? Ugh.
Also: Put merchant on node to collect if possible, redirect to one you can if not. Spam trade ships on that route so all their trade is drained to x node. Switch merchant to different node, spam more ships. Rinse repeat until all trade is blobbed to one node and collected by you. That's how you get a lot of income. Works best with end nodes like Venice/Antwerp, but still very effective otherwise.
I'm not sure if it's a bug, but stacks of ships that wouldn't be able to 'protect trade' on a node with no merchant of your own are not taken off the route when you remove the merchant. Makes it easy to redirect/collect from every node you come across even with the default 2 merchants.
Playing with Oman and 7th in world due to my trade income. Basically, Oman is Middle-East easy mode. Go ahead, try it.