If you increased Switzerland’s population density by 50% they’d be in a crowded hellhole like (checks notes) Belgium
There are significant differences in terrain that make that comparison a bit tougher.
But Belgium does suck. I drove from Amsterdam to Paris in the early 2000s, and Belgium stuck out as being obviously worse (dirtier) than the other two.
Yeah, but while Belgium is basically a huge plain, Switzerland is 60% Alps.
If you account for that, the effective density of Switzerland on the usable area is 600–700 people/km².