We're talking about a completely different story between Destiny and other games and potentially between pre-TTK and post-TTK Destiny depending on how the scaling works. If the implied level of disparity of being one level below held true in effect, it wouldn't be a big deal and would mostly be, as you said, identical to just making tougher, harder hitting enemies in all but psychological terms. However in Destiny being just one level below severely penalizes you in damage given and taken in a manner that doesn't match up with what one might expect from being "just one level below." Furthermore, this style of artifical difficulty ensures that when the level cap is raised, the difficulty is obliterated as this penalty is removed, which wouldn't be the case with "elite enemies" if simply programmed to be at "one level higher numbers." See what has become of poor HM Crota... Shrek and Fiona never even get to come out to play anymore with a half-decent swordbearer.
If this manner of penalty is smoothed out by the higher level cap and alternative Light system it might well be a much more negligible factor.
This is my biggest problem with how Bungie did CE, as well as PoE 35.
We get forced to be under leveled for the fights, and once you get at, or above the level, there is no challenge.
Look at Vault of Glass normal mode.
Even with a pretty good team, you could still run into wipes.
The encounters have more thought to them other than "as long as people are under leveled for his part, it's going to be hard!", the VoG was hard because it took more coordination, and spatial awareness.
Hard more is a little harder because of detainment bubbles, and oracles being harder to kill.
VoG is overall a better raid if only because of its varied game play, not just shooting, not just running, not just holding a spot.
I feel much more joy killing Atheon than I do Crota.