You’re ignoring that the UK is the locus for the entire continent’s financial services industry, an industry that creates a massive amount of wealth, taxes and jobs for the nation, and an industry that is leaving London because of Brexit. Goods exports are not really the story. Services exports are where the money is.
Except it isn’t. Since 2016 the city has expanded “despite brexit”. Regardless, if you want to understand Brexit, visit the provinces, were manufacturing industry has been pissed away by London and it’s London obsessed focus. A dip in the pound and opening free trade to the rest of the world is a great first step to rebuilding manufacturing.