One of the biggest issues with the current game is, for me, the sheer ludicrous volume of disposable gear that's effectively thrown at players. One reason this is an issue is because when you start to overwhelm players with items that make what they're wearing redundant, you effectively lower the value of every item as a result. More rewards makes the game, ironically, less rewarding.
The larger issue here is that the inflation of item level via raiding is effectively creating a huge communal split of haves and have nots. The bottom line is that a group that clears heroic raids will utterly outperform players that don't do organised raiding due to the scheduling demands that it has.
Here are some numbers:
Level cap quest rewards are sat at 281 item level, but we could probably throw in top end crafts and azerite to round players to around 290. World quests will inflate that quickly to the heroic dungeon requirement, where the item level is 325 for precious little effort.
This is already an 11% increase in power with effectively no effort whatsoever, assuming we're talking about 290 to 325. There's then a group of things that compete to increase that number (LFR/Warfronts/WQs/Mythic dungeons/Titanforging) prior to the progression PvE system that matters, in heroic raiding. Heroic raids are throwing out 370 item level slots, which in turn is a 22% jump in power from when you first rounded out at the level cap.
If you take that next step up, and consistently kill Mythic raid bosses, then the reality is that you'll be equipped in 385 pieces which is a rounded jump out of 25%.
So, in other words, if you're just generally dungeoneering and questing then you can expect a solid item level of 340 or so. This is thirty item levels behind the heroic raiders who are going to have pretty much an 8% advantage over you, outside of skill differences.
Rounding out, level cap players are already at 75% of power available in the first tier of this expansion.
To compare this to Classic, for example, the jump was about 60 to 90 at the absolute top end (which there were less of than today's Mythic raiders), so a third of difference through the entire version of the game. We're already close to that after a single tier.
It's just another reason to look forward to Classic. It's not just the additional depth that it has throughout its systems, it's the fact that you don't need to be at the absolute cutting edge in order to have decent development options.