Well, Phil, I'm glad you agree that when Brexiteering politicians spew on about "Participating in a court that applies EU law and is bound by the CJEU would be inconsistent with the Government’s aims of becoming an independent self-governing nation” you're admitting that they're being hypocrites, because obviously courts like ITLOS and ECHR and the WIPO tribunals are courts that apply non-British law, and only a complete idiot would fabricate some qualitative difference between non-British-but-European and non-British-but-something else. Britain is never going to be an "independent self-governing nation" if that means adhering to only British courts.
Obviously, Britain will adhere to foreign/multinational courts (such as ITLOS). So not wishing to participate in EU institutions is not a matter of some grand principle, but just classic "hard Brexit" doggerel: it's because they are _EU_, institutions, not non-British... (A sane Brexit policy would have kept Britain in things like the JAA while diverging in other areas, but that doesn't fit the dogma).
Meanwhile, _which_ countries are lining up for trade deals? Be specific. Use names. And apply percentages of trade... Remember, you've got about 50% (depending on how you measure it) to balance what will be lost with the EU. Of course, things that were manufactured in the UK for EU consumption will fall, because the regulatory framework (even if the UK manages to agree a deal with the EU, which is as likely as pigs flying at the moment) adds cost that a plant in, say, Ireland won't have. Don't count on the USA. Trump is a fan, Biden has more rational priorities. Don't count on China or Hong Kong, either, given the current diplomatic chill. So that leaves places like JPN, AUS, NZL, SGP, IND, TUR, Russia, Latin & Central America -- not to be sneezed at, but all a long haul.
And yes, I agree the UK has done better than the Eurozone... but that fact rather defeats your thesis that the UK has been dragged down. Surely an equally valid explanation is that, being a non-Euro economy, the UK offers the best of both worlds.
I hope you're right about Scotland, but the evidence isn't compelling. Every objection you make applied equally to Scottish independence, and yet that was far closer than expected. And the Brexit decision proves that people vote for nebulous intangibles ("taking back control", who f'cking cares about whether Edinburgh, London or Brussels "controls" as long as the results are palatable?) in the face of obvious economic risks.
[ Incidentally, while the Channel Islands were indeed never formerly part of the EU, their trade with France was controlled by London, which was. And Channel Island/EU relations _was_ a part of Britain's EU membership, so they've already experienced the chaos caused by Boris's talk-first-think-later scheme. People in the Channel Islands and also Gibralta look at Malta and go "Hmmm..." the thought of an "associate EU membership" (which doesn't currently exist, but could be modelled on Norway or Switzerland) is not unappealing to many. ]