Calling it "default" or arguing over whether it is the "default" is what is meaningless. It doesn't matter. You are absolutely correct that most of the WotC adventure paths were written in Faerun locations and that odds are that people who do not create their own setting for their game will use Faerun over other previously published ones. No argument there. But so what? Why does that matter? It doesn't. So the folks here having pissing matches over "Faerun is the default setting!" "No, it isn't, it's the D&D Multiverse!" so on and so forth are just arguing over nothing. Because no one will eventually accede to the other and say "Okay, you are right.", and even if they did... again, so what? That's not going to change WotC's behavior. WotC will still to do what they do regardless of what gets "agreed upon" here on the boards.
Of course people are still going to argue here about it if for no other reason that it's something easy to argue about and why else are all of us posters here if not to just argue meaningless arguments because we have nothing better to do? LOL! Heck... MY post was a meaningless post too! I can admit that. My post that asked "Why are you all wasting your time arguing about this when it doesn't matter?" is just as much a post of me just filling my time as your post was countering mine. So it's cool. We're just talking for the sake of talking because why not? Beats working.