A slightly puzzling thought here:
Of course a privateer statelet like Singapore or Hong Kong can get rich that way. The upper bound seems to be approximately Switzerland, and plenty of smaller states ain’t no Switzerlands. Britain is well above that upper bound.
So, small states and small states only can prosper by having low barriers to trade with hte rest of the world. Large states cannot.
But large states have no internal barriers to lots and lots of trade among their large population. Something which makes those places richer. The internal economy is always much larger than any international trade.
So we seem to be saying that tariff free no barrier trade is just super except when it crosses national borders. Which doesn’t seem to work either as a piece of logic nor empirically.