I feel like people have unnecessarily cluttered UIs. Honestly, if you're a DPS, you don't need to have your party member HP bars showing. If you're casually raiding then you don't need DPS meters. WoW rotations aren't stupidly complex like FFXIV rotations where you need to have 3 bars filled with 40+ different abilities; you can usually fit your rotation onto 1 or 2 bars, and still have room for other stuff like mounts.
Where WoW fails at is informing the player what is going on. Boss and mob mechanics are not standardized or intuitive, nor do they have tells/wind up animations. Many boss abilities have a bizzare mechanic that you cannot possibly learn from observation, and require consulting an out of game guide that explains to you how the mechanic works. Or you have to install DBM, which is very unimmersive because you're constantly hearing an airhorn or the "run away little girl!" voice line. And there are so many mechanics going off that if you die, you have to spend several minutes looking through your logs to figure out what killed you.
One thing that FFXIV does very well is mechanic tutorialization and standardization. Most bosses in the game use some variation of the same ability, and the mechanic specifically unique to a boss is very clearly demonstrated to the player early on in the fight before the mechanic is layered with other mechanics. There is never more than two or three mechanics going off at a time (never more than 2). I never felt confused by what was going on, and if I died it was obvious what happened.
The other problem with WoW fights is that there is too much visual noise going on. It is hard to see where mobs, NPCs, and other characters are, so you have to keep their HP bars turned on and label them with obtrusive markers to see their position. In the screenshot I posted, there is a NPC you have to keep alive or else you fail the fight (Kor'vas), but he is standing in a green puddle and you can't even see him, only the orange marker on him, and this is a pretty mechanics light fight compared to your average raid fight.
GW2 is 20x worse than WoW, though. In that game you can't even see if you're standing in an AoE or if a boss is about to hit you.