Many people get sober without AA.
I have no statistics...but I bet that most people who get sober (long term and happily) do so with some sort of help...counseling, AA or another group program, rehab, etc. My guess is that only a small minority successfully quit, long term, "on their own."
Not saying it doesn't happen; of course it does! But from reading here, and from experience, will power alone isn't enough for most alcoholics. I've quit in the past for months, even years, on will power alone...but was not truly sober and always went back to it...each time worse than the time before, too.