I would think that for optimal citizen mental health, you want something like a honeycomb: citizens should ideally have 2 parks within walking distance of their homes where they can get outside, relax, enjoy nature. Similar principles apply for coffee shops, grocery stores, bars, and many other amenities: you can get by with one within walking distance, but you ideally want at least two options to insulate against closures, times when one is closed or too busy, or in the case or parks, when a large event, like a public market or a concert, is happening in one.

I can say from experience in NYC: Central Park is nice, but one giant park for a large chunk of manhattan is not ideal. Works fine for UES/UWS, who have other park options on the island coast. But the section down near Midtown is miserable. And “parks” in the rest of the borough often don’t even have accessible grass (it’s fenced off, as if it was a garden or something).

There are problems in my current city, Denver, as well. But parks are very pleasantly pockmarked around the city to give residents options. Now if only they’d close off the biggest park to car traffic…