There's a difference between a grind and a gate.
A grind is fine if its done well. Gear grinds are fine, they're a base function of the end game.
The problems lie when the game forcefully stops you from progressing somewhere and makes you just wait to do it later. Suramar's entire story is this.
I'd say a grind that is done kind of poorly is the upgrade from Normal to Heroic dungeons. Its just the exact same thing slightly harder. This is why I'm hoping mythic+ actually makes the hard dungeons interesting. Heroics should have added a mechanic or more to every boss fight, like they used to do. That on top of the even further increased difficulty and mechanics that Mythic+ offers makes Dungeons actually feel like an alternative to raiding, right now it definitely does not.