Screen time (which I know I had too much of, to my lasting detriment) displaces other, better activities. Seriously.
I spent most of my time from 10-16 reading books and computer screens, both solitary indoor activities. However via a computer and a modem I communicated with hundreds of people regularly. I don't see that as lost time.
I feel that the average persons home would generally be within walking distance to some sort of public open area.
As a parent it takes more energy, inventiveness, and patience to entertain our children (or on that note, even another adult) than it does for ourselves.
These alternatives to screen time don't come easy.
My kid isn't that old, but I got them a robot that they can "program" from their iPad, its solid learning and exploration time.
I think we need to differentiate between "zero value screen time" and "learning screen time" before we make any real judgements about it.