Re: "the opportunities created by Brexit".
"What we should have done long ago is form a national Brexit strategy committe that consults with UK industry and decides in what sectors we want tariffs and in what sectors we don't, then used that to negotiate a UK-EU trade deal. "
This bit is absolutely correct, and even I, as a staunch Remainder", am mystified by the lack of planning. There was no need, or sense, in going for the earliest possible leaving date - spending a little time actually finding out what was needed, and maybe even asking the population what was good/bad about the EU would have avoided all the clusterfuck since then.
"Unfortunately our politicians have made a complete shambles of Brexit thus far, but that's their doing and not the fault of Brexiteers."
I'm calling bollocks on the assertion that it is not the fault of the Brexiteers - the lunatic rump of the Tory party plus the high-pitched whining from those now known as the Brexit Party - would not have allowed anything other than "action now!" To actually think about what is to be achieved would have been a "betrayal of the people who just want out". Look at the posts here by @codejunky for evidence of this.
"Since joining the common market Britain has been in steady economic decline, we've lost many large companies, run up a huge trade defecit, seen our relative world standing fade, while in real terms our young people are poorer than they were."
None of this has anything to do with the EU, and everything to do with successive useless governments in the UK. There is nothing that the EU have mandated that required large companies to be sold, a deficit to be run up, or the futures of young people to be trashed. The latter can be squarely placed at the feet of unnecessary "austerity measures" imposed by bastard Tories, but before that, screwing with education such that e.g. languages were deprecated (difficult to work abroad if you can't speak the language), and science was Elfin Safetied out of any use. Our relative World standing can also be placed at the feet of UK politicians following the lead of the USA in meaningless Wars Against Stuff, and acting immorally whilst doing so (torture, killing civilians, lying about everything (e.g. WMD))