There's no way to profit from trade downstream.
That is simply not true.
If you can gather enough trade power via ships or provinces, you can stop the flow in any node and collect from there. Of course not every node works for this, but that's just realistic.
Yeah, holding land is the only way to get trade power. I guess you can consider building light ships, but in practice they cost maintenance, force limit, and are an awful investment compared to anything else. If you don't have 50% of the trade power in a node you might as well ignore it because it's a waste of time in EU4.
Again, simply not true.
Light ships more than pay for themselves if you send them to a worthwhile node (especially a hundred years in, once their trade power increases). If they cost you more maintenance than they gain you, you are simply using them wrong.
And force limit? Who cares? What else are you going to use it for? You need a certain number of transports and heavy ships (and in very rare circumstances, galleys, but I never found them worthwhile outside of Italy). More of those just don't serve any purpose, so you build light ships and earn dough with them. Very much including in trade nodes you have no provinces in.
You have to check every available node to figure out whether it's better to send a merchant to collect, a merchant to steer, or no merchant. You have to check this in probably a dozen nodes by mid game, the combinatorics is ridiculous. You have to check constantly because an AI might decide to stop steering your way which means you need to put a merchant there to get it your way.
Needing to check on something constantly is awful. In computing terms EU4 trade is a system that requires polling, a good system is interrupt based. Meaning, if something goes wrong the player should be notified to fix it. In EU3 if things go wrong your merchants flatline at zero because they all get competed out, letting you know you are probably trying to trade somewhere you can't compete in. In EU4 you just silently lose thousands of ducats until you enter one of the 50 map modes to math out what changed since you last checked. It's a bad system for any high level strategic game.
I agree the feedback could be much better. But I never needed to do more than notice there is a sharp drop at one of my collecting merchants, and then look downstream for causes until I find them. That happens every now and then, but simply not "constantly".
If you fail to realize for years that you lost lots of money, you should be blaming yourself mostly, not the game.
EU4's CoT and other modifiers are basically irrelevant unless you want to border gore everywhere or do something ridiculous looking like taking only coastlines. You might take them slightly earlier than nearby provinces but in the end you still annex whole regions because that's how the game is designed, you need to monopolize nodes (and the state limit now punishes taking lots of unrelated territory with -75% tax and production). In EU3 all you needed was trade range, two or three trade ports across the globe to get a piece of trade anywhere you could compete. Which made sense, IRL trade nations didn't need to take the centers of trade in every country across the planet to make money, they just needed access to the markets to initiate trade. In EU4 the trade zones in China or India are basically useless until you've conquered a quarter of the provinces, enough to get a new merchant and either send it back home or collect on site.
Your entire argument revolves around the notion that you couldn't gain a profit in a trade node unless you have a big chunk of provinces.
I have spent hundreds of hours in the game - with either VeF or MEIOU mod, but I doubt vanilla is entirely different in this regard - and that assumption is simply wrong. Of course having provinces helps, but you can gain a nice profit even without any as long as you have at least one port nearby for your light ships to go to.
You either need lots of provinces at a node or be able to send lots of ships there, both is of course optimal, but either is enough for a good profit.
I don't exactly remember the EU3 system, but if you could gain a profit there without either having lots of provinces or lots of trade ships, it didn't make any sense at all - where did the profit come from, if not from your ships or local presence? Magic?
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. Also a lot of game experience helps a lot.
