Partly true.Yes. There are feral packs in places. Hawaii is great example. I live in FL, have most of my life. Commercial chickens don't thrive here, most breeds completely unsuited to our summers and our predators, and are quickly eliminated. What survives as a feral pack does not thrive, though a few birds eke by. If you bought them from a breeder, you would almost certainly complain of the sub par quality of weight gain and frequency of lay.
Feral chickens are in general of a slimer build than the usual American back yard favourites.
Yes, what little research has been done reports a gradual decrease in egg production. One hopes this is the chicken readjusting from the high production breeding programs.
There are feral chickens in great numbers in many places in the world; just not in the USA perhaps.