Except the whole reason this debate comes up is because even the hard modes are subject to ridiculously deflating blanket nerfs for the sake of EVERYONE seeing them. I doubt most people who call the game too easy haven't gotten to experience it (since at this point nearly everyone who wants to has done so with that kind of completion rate). If it worked as you noted (the logical way) there wouldn't be issues.
Bingo, I'd be willing to bet that quite a few of those complainers haven't done a bit of raiding outside of LFR>