After building a 50K following on G+ the first 2 years, and after that following went dead over a year ago... IF I had put that time and effort into, and SOLELY into building an email list?
My fiction would be best sellers and my business would be making 7 figures. What most don't know, is it only takes a 15K list of readers to be a best seller and it only takes a 30K list of subscribers that buy to make that kind of money.
But as far as FB goes, my email delivery clients are on FB and engage ONLY on FB. Hence I moved there 6 months ago and am making $10K a month off consulting. And that is from ZERO in just 6 months.
Really, it depends on where YOUR audience is. For me that is advertising my fiction on the big book blogs.