Depends, small cities if you're there to just see the "sights" you can easily do it in the three days. However the worse is when you see this being said about large cultural cities wtf how fucking uninteresting of a person and cramped schedule do you have to actually think this, it pisses me off.
I really like history art, architecture, urban planning, and cool engineering infrastructure. These are the three things I spend my time on. I also enjoy spending days just walking around chilling people watching as I enjoy the vibe, maybe going on a date and meeting people at night. I really take my time with everything, I hate being overwhelmed. I go to museums I like multiple times on trips because I'm slow. Three days in, I've barely gotten settled
Cities like Istanbul, Florence, Rome, Paris, Hong Kong, Tokyo, Mexico City, Madrid, London, St Petersburg, Beirut, Tunis, New York, Chicago, San Paulo, ect. I like to spend at least a month in. Smaller cities, I usually go two weeks. I cannot imagine 3 days in anything but a village