It's a good thing the UK is less "relevant" than in those days! It would not be better for the world or for Britain if the British Empire was still at its peak. After all the Empire was wound down deliberately, the people didn't want to continue with it.
"The US and the EU, at least, are exporters of rules and standards in the way that the UK is not (it effectively was when it was a member of the EU, as it had a lot of influence on the EU position)."
No, that's a common claim but not really true. The UK had very little influence inside the EU and the EU rules were almost always made to satisfy the needs of either the EU institutions themselves, or the domestic economies of France and Germany.
A good way to see this is to look at the fate of the "single market for services". The UK is uniquely strong in the services market, so guess what the EU never made much progress with? Compare to its obsession with harmonizing everything to do with goods trading, which benefits primarily Germany.
Another way is to look at how responsive the EU was to the concerns of British voters on immigration levels. Answer: they hold voters in contempt and weren't willing to budge an inch. There was no influence, that's why the UK voted to leave.
"As for trying to survive, Brexit has bolstered the Scottish independence and Irish unification movements"
The latter maybe yes. The former, probably not. Scotland would have to apply to join as a regular country and its finances are in no state that would allow that.