I can't speak for everywhere, but at least in Seattle, most of the helicopter parents I see and know are not millenials but genX. I'm on the upper edge of what is called a millennial, and almost everybody I know that is younger than me is very intentionally hands off.
Curious, do you have kids & if so, are you doing the hands off thing?
I live in Seattle (within city limits) and would love to chat with someone about how the hands-off/free-range thing is working in practice within this city.
I don't see any evidence that free play is increasing as new parents are coming on line. Things look even more structured and over protected than ever.