> Which is impossible to do properly, because those keyboards differ from US keyboards in their geometry, not just in the labeling of the keys.

The only difference is that on US keyboards the enter key is smaller and left shift is larger, leading to the "\" key being moved one down and one left on a German keyboard (and also being duplicated to left of z (German label: y)). So even if you move from a physical US keyboard to a physical German one while keeping the US layout, it's literally just one key where you'd have to retrain your hand. And for people that have learned to type on a German keyboard this is not a problem at all since they have never typed on a physical US one and using a different mapping means a training period anyway.

Source: German who mapped his keyboard to US (+ some AltGr modifiers for the German characters I need).

I don't know about the other European layouts, but I assume it's somewhat similar for them too.