"I think this is a bit misleading because the argument was never that Brexit would cause an instant Mad Max-style collapse visible on a GDP graph."
Recollections may vary.
"Even the OBR still estimates Brexit will reduce long-run productivity and trade by around 4–15%, and the recent NBER paper estimated a 6–8% hit to GDP by 2025."
Estimates and calculations. But impossible to prove. And no doubt biased with a political agenda.
"Tthe figures quoted don’t exactly show the UK outperforming comparable economies."
No, they don't show the UK as outperforming. Unless you want to throw Germany into the mix. They show the UK pretty much performing the same as comparable economies. So no disaster there then. Pretty much same old same old. Despite Brexit. Of course there are people out there that would claim that without Brexit we would be roaring along at the 15% increase the US has had. I remain skeptical.
"the Eurozone overall has actually grown more since 2019".
Yes by about 1% over 6 years. We aren't exactly talking huge differences here. If it were the same difference as between the UK and the US or the UK and Germany there might be some sort of legitimate claim.
"Germany struggling doesn’t suddenly make Brexit a success."
Yes. But it does show you that economic performance can vary considerably even if you don't leave the EU. So attributing economic changes unambiguously to Brexit is really hard. If we had performed as badly as Germany over the same period, would people be attributing that performance to Brexit I wonder, and would that have been a reasonable analysis ?
"And “we’ll replace EU trade with the US and Asia” was always the theory, but years later there’s still little evidence it has offset the loss of frictionless access to our largest nearby market."
Well, other than the fact a lot of people said Brexit would lead to poor economic performance - and it clearly hasn't - or not in any way that someone can reasonably prove. So what is the real explanation for that ?
I agree re the benefits of the US/Asia Pacific market are yet to be established. In theory there are better opportunities for growth in trade there. Practice may be something different. Once again it will actually be difficult to prove if economic performance does take off over the next few years whether that is due to US Asia/Pacific trade or maybe other things. As before, I think it would be a bit crazy now we are here not to see how the opportunities develop.