So in the UK we have 2.5mm^2 wires in a ring on a 32A MCBs... Of course a 2.5mm^2 wire is rated ~20A so any issues with the ring (sockets still work since connected from the other branch) can burn the wire before the MCB trips...

From what I understand the UK allowed it because of a severe postwar copper shortage and it persists to this day because it's allowed and a bit cheaper.

I'd say "severe post-WWII money shortage". After wartime expansion, the global copper industry could physically meet peacetime demands. But the UK was very close to national bankruptcy. And the Luftwaffe had turned an awful lot of their prewar housing into rubble. So - any cost that could be cut, was.

If you plug it into an overloaded ring final (which is not uncommon in the UK - half our house's sockets are on a single ring), you have to rely on the generator being able to detect faults to protect that circuit.

You could also overload that circuit's wiring. If you have a a 16A Ecoflow, plug it into a 32A ring, you could draw 48A before tripping the grid circuit breaker, potentially causing significant heat in the wires. Dinky 3A generators won't do that but I don't think they're the limit our government are talking about.