If I were to do a fresh build, I’d likely do it your way. I renovated our older home a few years ago and had to basically add another pocket on the inside of all exterior wall to insert insulation. The heat loss without it was massive in the winter months. Utility bills were close to four figures in the cold months.

Mine in 1915. Solid too. Just because code is less stringent, doesn’t make homes unsafe.

Not sure about US housing being unsafe compared to German housing stock, but it’s certainly flimsier in general. Housing nowadays in the US is mostly built to last 30 years. Solid interior walls are very unusual and concrete floors are rarely found on buildings less than 5 stories tall. Timber framing clad with siding is commonplace in the US where brick exterior walls are mostly used in DE.

It’s no worse in various countries in Europe than anywhere else I’ve seen. The old mantra of throw money at the situation if you want something better applies.