The population of Switzerland is ~9 million. The population of LA metro is around 15 million, and NYC metro aroound 20 million
LA "the city" might be less but you can't tell where LA ends and it's other parts begin. It's one giant metropolis. Same with NYC.
The city of LA is just there for administrative purposes. People who live in "Burbank" or "Pasadena" are seen as living in "Los Angeles" by most people outside the region.
You can tell where the city ends very easily. There are well-defined boundaries. Government statistics take that into account. Here's the census page for the city of Los Angeles, which lists a population just under 4 million: https://data.census.gov/profile/Los_Angeles_city,_California...