I lived in a mountainous area of Italy (very narrow roads, full of ups and downs) so I am a fairly confident driver (probably why I was not too stressed driving in Italy) and drove in countries like India and Iran in the past (so very familiar and happy with slow, but very crowded and unpredictable traffic).
To clarify, the anxiety we had on Autobahn and Swiss' highways was not a reflection on the quality of the roads, and more a reflection on the driving 'style' combined with the speed that those roads allow. The style was quite aggressive, very fast in every lane, loads of overtakes (car constantly zig-zagging), people coming from the back _FAST_ and staying there, people switching lanes immediately after signalling rather than giving some time for people to notice. Overall, that combination made for a very stressful experience which we have agreed (as family) not to repeat in the future.
But then again we have 0.1% of information to make a good picture of your situation, driving skills and habits, vehicle you moved around and so on. But there is for sure a good reason for such discrepancy, ie driving caravan super slow or similar tiny little detail.
Also you magically skipped few (pretty horrible to drive) countries if you had a road trip that covered Greece.
Maybe one thing that amplified the effect was the high expectations we had for those highways, and maybe that's what made it more shocking for us.
Again, I consider myself a 'decently skilled' driver, having driven in many countries over the course of the years, and easily adapting to driving styles (US/Italy/France/Iran/UK/India/etc). Some of these styles are indeed chaotic, but they (generally) operate at slower speed, which allow for corrections and precautions. The thing that threw us off is the combination I have mentioned before:
> [...] the speed that those roads allow. The style was quite aggressive, very fast in every lane, loads of overtakes (car constantly zig-zagging), people coming from the back _FAST_ and staying there, people switching lanes immediately after signalling rather than giving some time for people to notice. Overall, that combination made for a very stressful experience which we have agreed (as family) not to repeat in the future.
The German situation seems vastly superior on the basis that whoever is the "odd one out" or violating the norms should be the one having a bad time. Basically incentivizing homogenous and/or predictable traffic flow, which is safer.