I personaly see this totally different.
The "traders" buying the goods from your customhouses still need to pay the same taxes in the mother country.
They simply hand them through to you.
So why should they suddenly pay you higher prices for your goods, if they still pay the same taxes in the mother country ?
Please excuse but simply because
you think, that something should / must work a certain way, this doesn't mean it is the only truth.
(There might be many different opinions and ways to look at it.)
Please slow down with phrases like "weird" and "nonsense".
Indeed, but the same applies to you, this is not because you think it is right, that it is right.
I tried hard for 10 mn to see if your view was the best of the two, but sorry I failed. Have you done the same for me, or did you discard at once my opinion? Have you tried hard to imagine that may be, your way of seeing is not the most logical way, for this particular feature?
I guess you are also happy that the market behave in a non nonsensical way (not an insult, sorry!), unless you tell me that it is normal that selling 800 cigars alter the price of tools, right?
As for the King's tax, let me rephrase (or repeat). The facts are what, let's get to the basics...
The King ask you money, if you refuse, the tax raise. Sometime he also raises the tax, for various reason, like sustaining his navy etc. De facto so, the tax level is strongly tied to the policy of the King of your mother country toward the colony, specifically. It does not mean that the taxation level is the same between the mother country and say Prussia is the same. Historically, tax on import could differs for each country, it depended totally of the foreign policy toward said country.
Then you declare independence. You are free from anything the King imposes of you. If you manage to sell merchandises to Europe, it can be to any country you can reach. Prussia, Austria, Venice, England (if you play Spain or France), etc. But still, you still suffer from the same exact tax. Just try to give me an historical, valid reason to that!
So sorry, I'll keep using the word non sense, or if you prefer 'lack of logic'.
Now, my second point, equally valid, about why the tax level should not be exactly the same. Not changing this tax level when you get independence leads to a poorer game design, because it removes one option from the panel of strategies you can imagine when dealing with the King. Why? Because as this is the same tax level in the end, you don't have any choice but to say yes to the King, each time, while you are a small colony. Failing to do so result in very high long term taxes, even when independent. The only viable strategy is thus to maintain as low as possible the tax level, so that during independence it is still valid to trade with Europe.
As for not needing money during independence, I beg to differ. When you play on highest difficulty, with a King's army of 600 personnels, speeding up various buildings or artilleries, or forming specialists or veterans still costs a lot of money and is very necessary to beat the King.
Again, everyone is allowed an opinion, this includes you, this includes me. I think you are wrong. Perhaps I'm wrong in that
but still, this is my opinion and I have the right to express it.