Even if I used Facebook, I wouldn't call it a 'good product.'
It was a good enough product at the time, and the rest is history. As you point out the biggest competitor at the time was MySpace, and comparing it to a collection of geocities pages is being nice. Really, really nice.
MySpace was DML, Diarrhea Markup Language, an unholy union of HTML and something more ungodly than Satan himself splattered across a web browser. Its almost as though someone thought that the blink tag was the best thing since internet pornography and went from there.
Once it took off, there was no stopping it. The entire point of a social network is the number of people in it. It doesn't matter if Google+ were thirty times better because no one uses it and it has failed to hit critical mass. The entire point of the product is that everyone you know is most likely using the product, which makes it insanely useful, even if everything else about it is pure ass. Mind you, not Natalie Portman ass, but 350 lb. trucker ass.
So in that sense, Facebook is the perfect social network platform. It has almost everyone on it, even if they're no longer active. Hell, even though they still can't actually find Jimmy Hoffa, you can find him on Facebook. In that way it's not just a good product, it's an insanely good product.