There's just one problem with that theory: it doesn't fit the evidence. Single Abstract Noun is a guild that is as full of friendly, helpful, sociable people as you can hope to see. If there is a progression raider there, I haven't met them yet. So if this theory were correct, you'd expect these hopeless social types to be worse than the average player, because they're certainly more sociable.
Fortunately we can test this theory pretty simply. Compare the success rate of guild runs with those of random PUGs. You know, the ones where nobody speaks and is only running it for the selfish purpose of getting loot (or emblems) for themselves. That's about as anti-social as you can get, so they should perform better, right?
Of course the opposite is true. SAN guild runs scoot through content that's many levels above them with no deaths, no wipes, no problems, all the while chatting away and being friendly. This isn't because we're a bunch of twinks who outgear the content - most of the players are in whatever mix of whites & greens they have picked up from levelling on a new server. Meanwhile the anti-social PUGs wipe & fail continuously, even when they are many levels above the instance in question and are twinked to the bejesus with heirloom items. Since joining SAN, I've done 5 guild runs & 5 PUGs. Guild run success rate: 100%. PUG success rate: 0%. Not one of the PUGs has made it even to the first boss.
So what makes these socials so good? They talk and learn from each other. Because it's a friendly environment, they aren't afraid to say when they don't know something, because they won't get kicked for being a n00b. Instead other players who have more experience of playing that class on an alt can help them learn the tricks of the trade. More importantly, they care about what happens to their guildies, so they try harder to avoid letting them down. Playing with people you like and respect improves your performance, it doesn't hinder it.
Its those anti-social "gogogo" types that struggle.
Edit: The "dumbed down WOW" cliché is heroically revisited by Klepsacovic here. Kids of today ... good old days ... national service ... it's the only language they understand.