Cat's in urban areas that aren't socialized are always skittish. It's about not being socialized to humans are a critical age. The areas that you are finding "friendly" strays are where people abandon former pets. Former pets were socialized at the critical age and want human contact.
Basically you are describing areas with shitty humans as areas with superior humans.
If your little murder floof is on walkabout, it's either unplanned or you need to re-examine things. If you want fewer mosquitoes, keep your cats inside 100% -- that's almost a binary choice.
The world has changed; and any cat outside should be seen as the indication of a problem. Also, depending where you are - eg k2k - the coyotes or similar indigenes will handle things in ways you don't want.
I, like many, will have to disagree. This is just my personal opinion though.
One of our cats we let out whenever she wants, she desires being outside and I can't seem to steal that freedom from her. I know it's more dangerous outside, but she was a stray for the first couple years of her life and is probably more aware of the dangers than most people. Now she mainly just sleeps in a chair on our porch watching birds.
Our other kitty has always had a home and loves outside, but only goes out on a leash (before her I honestly didn't think a cat would use a leash).
Cats still do well outdoors in rural areas. Disneyworld is proof of this. Every night, Disneyworld fills to the brim with cats, and the park decided to use this to their advantage to keep mice out. They don't live as long living their life outdoors, but it's not urgently harmful to them either.
The majority of human beings live in urban areas where its ridiculously unsafe for cats. In the city every outdoor cat is either abandoned or feral and neither particularly long for this world.
Outdoor cats live about 3-5 years, indoor cats live 10-20. Again shitty humans.
That, as you implied, depends on the environment. In a safe rural setting, which are not as depopulated as one would think (would people complain of rural America for example if it was a drop in the bucket), it's more like one to three years less than the average indoor cat.