The game doesn't have the same difficulty curve due to gear creep, and ARR content really is a push over, even when levelsynced. Only the players who played 2.0 at release, actually got to experience the entire game at a difficulty level that made sense. If you played a healer from the beginning, you also got to experience every solo fight taking 10 times longer.
To get that experience again, you have to play the new content on the first day it's out, and if you've overgeared it already by playing the raiding content, then you also don't experience it at the difficulty level it was designed at.
Where the game needs to fix or adjust things is to have the "minimum ilevel" be the default setting until the content is cleared by everyone in the party. It's painfully awful to play LotA/ST/WoD now and have players wipe to mechanics because they try to skip them. Like both Scylla and Glasya Labolas in Sycrus Tower, don't even get to their main mechanic. Some players even survive Xande's Ancient Quaga, when that was an instant KO before. At least WoD's mechanics aren't particularly cheesed by gear creep.
Which is to say, I don't think all content should be raid-tier hard at all times. Rather I think new and returning players are robbed of any satisfaction in clearing content if the content can be completed by overpowering it. That's the very problem other MMORPG's have. It's not as bad as other games (which are equal to running everything unsynced), but they present little or no challenge for the reward given. If LotA and Rabanastre have the same reward, but different difficulty, then there is no incentive to play the hard content when the same reward comes from the easy content.
