There are two huge problems with this game.
Weekly lockouts are one. A lot of people log on for a couple of hours to do raid finder and various other weekly things, then don't touch the game after those lockouts are in place. If a player wants to do content to earn gear, let them. I understand that you don't want people playing 70 hours straight to earn best in slot, but you could at least think about adding some type of "diminishing returns" for loot (let me specify, a player can always do whatever content they want to do, and there's always a chance for them to get the loot they want, even if the chance to get that loot lessens with each run, but never reaches zero). It's never a good idea to tell your players that they can't do something they love doing.
The separation of PvP and PvE is number two. Splitting the game down the middle was not wise, the game was SO much more connected in Vanilla. Players got to see both sides of this glorious game, but now you have to pick PvE or PvP as your main focus. This hits even harder on casual players, because they don't invest the time to master both play styles, and collect both gear sets.
Obviously these are my opinions, and I'm sure many disagree.
I absolutely agree weekly lockouts are one of the biggest problems. If I skip dailies (as I do), I only get 1-2 hours of LFR a week and then I'm done with WoW on this character. I used to enjoy running dungeons to get a few valor points so I can get gear down the road, but that's gone now.
On the PvE/PvP thing, I would like PvE gear to work as intro-level PvP gear like PvP gear does for PvE. A little PvP power and resilience on PvE gear would go a long ways to lowering that insane barrier to entry.