delericho
Legend
If there's no difference, why do you want elites put in the game that manages just fine without them?
Because...
The problem with having a single metric (level) for NPC power is that it then affects everything - the character must have better attacks, better defences, be more skilled, and so on. But that's very likely not what you want, because if you boost the attacks he becomes too lethal for the PCs, or if you boost the defences he becomes untouchable, or if you boost the skills, he gains access to powers that really don't fit.
It's also worth noting that 3e, in particular, already had a method for creating "elites" and "solos" - the DM did it by boosting the ability scores of the creature, with the knock-on effect to all the various totals, and a commensurate increase in CR. But that was always a crude measure - not only did it involve fiddly adjustments to the maths, but it also tended to create 'lopsided' challenges, allowing the PCs to strike at the weak-points, defeat the creature too easily, and thus reap undeserved XP awards.
(Incidentally, although it's not formalised, earlier editions also had similar approaches: the entries for humanoid monsters tended to read, "For every three orcs encountered, there will be a leader and three assistants. These orcs will have 8 hit points each..." or "They fight as monsters of 2 hit dice (THAC0 19)." For reference: Monstrous Manual 281-2.)
D&D has never managed without elites and solos in some form. 4e merely formalised it.
5e might be able to manage without. But past evidence suggests that the odds are very much against it.