> That’s a uniquely US issue - in NZ you can get a 100A single phase at 230V nominal without any issue. 23kw, straight to your door

In the US it's common to get 200A 120/240V split-phase service. We're talking about the wiring inside the house, though.

How do you think everyone here is charging their electric cars at home and running our AC and electric cooktops at the same time if we didn't also have that? :)

You need to derate for constant loads here, and I assume you have to do that in NZ as well.

So, no, not a "uniquely US issue".