You seem to believe your Scottish example makes you some kind of latterday Cicero, effortlessly dismissing counter arguments. It is a ludicrous comparison. The UK as a political entity has masses of data to make a comparison with the before and after effects of the first trade deal in history to introduce rather than remove obstacles to trade. Scotland has little of this, would be seeking similtaneously to join the European Union and putting the very same obstacles between it and England and Wales that the Withdrawal Agreement establishes (give or take the likelihood of a Common Travel Area).
But we don't need distorting hypotheses to draw conclusions so far. Experts given the responsibility have done the hard work for us. So when the OBR says “The latest evidence suggests that Brexit has had a significant adverse impact on U.K. trade, via reducing both overall trade volumes and the number of trading relationships between U.K. and EU firms,” or
when the Deputy Governor of the Bank of England says “Brexit … has been something that has pulled on our potential output in our country and that’s been our assessment for many years,” “We’ve not changed our estimate of the long-running effects, but we’ve brought some of them forward and we think they’re probably coming in faster than we first expected.” or
when the Governor of the Bank of England says "Brexit was one of a series of significant economic shocks to have had an impact along with the Covid pandemic and Russia’s invasion of Ukraine and the ensuing rise in energy costs.“These shocks have held back both productivity and labour supply,” or
The Office of National Statistics shows that we are the only major economy still to return to positive growth after Covid/Energy Crisis these institutions are using hard economic data rather than a ouija board.