That would be quite a lot of appropriate considerations ;-)) Even if customs duties / tariffs were originally a kind of pass money, today they play a completely different role in the international movement of goods: steering and control, punishment or incentive... Within a customs union, the same mechanism works, just differently...
You may well be right, but...
While chatting with ChatGBT I asked about the tariffs on passenger cars imported into the U.S. from the EU. Interesting enough it pointed out that as of early 2025, the United States imposes a 2.5% tariff on passenger cars imported from the European Union. This rate has been a point of contention, as the EU applies a higher 10% tariff on U.S. vehicles entering its market.
I just find it interesting.