I'm actually still using the approach that you describe - having assets in size 1x, 2x, 3x and using the ScreenSetup class. It will be rare that a device will really use "1x" assets, but IMHO it's very handy during development, because you can test the app in a very small window. 😉
Furthermore, at least in the tablet market, there are still some around that have a low density screen, where 1x might really be useful. (Looking at you, Amazon Fire Tablet.)
The whole notch detection thing is still a little confusing for me ... I actually don't know if Harman has simplified this since I last checked?