Yeah, it's crazy. When I went to visit my cousins in Paris, I stayed for 19 days, and it was awesome. A friend said that 3 days was enough, and it would be nice to travel to a few other places too. Maybe enough for a quick glance at some tourist spots, but not to actually experience the city. I could have stayed for a whole month, or two, and would still be getting new experiences.

As you mention, there's a good balance, and maybe 20 days could have been spent in 2 cities. But a weekend is very shallow