Brexit is widely regarded as both a failure (in the UK) and a cautionary lesson (in the rest of the EU).
Interestingly, the inflection point seems to have been within months of the UK actually leaving (while the UK formally left in Jan 2020, nothing changed until Jan 2021).
I'm curious to understand why those vulnerabilities existed in the first place .. and why weren’t they patched? also once you get hacked, its a sobering experience and u invest more in fixing the root cause .. so net net .. even with your narrative, brexit has been amazing for Great Britain (the best country in the world imho)
Remember, a lot of brexit voters voted for, essentially, a completely fantasy situation; they thought they'd be getting a situation similar to Norway, only with no free movement and with opt-outs from all rules. The EU was extremely clear from the beginning that this was not on the table (it never made sense in the first place; you can't have a single market where one participant is excused from following any of the rules), but Johnson et al were telling them that was what they were voting for. The hard(ish) brexit they ended up with is very much not what most people will have been expecting.