Regarding time over skill, there are still plenty of 3 day a week guilds that are doing heroic content as well. Not necessarily top 25 or whatever, but it's still doable. I would say if guilds like ours had 7 days to play, 12+ hours a day, we could probably kill a lot of things too.
But there's DEFINITELY a skill gap between these types of guilds, and ones that raid a few days a week but still are considering Normal mode their progression path.