The campaign isn't gameplay, the campaign is the story arc of much of this expansion. That's why it, you know, revolves entirely around advancing the storyline.
As for Legion being praised as the best expansion since TBC or Wrath, that's just a pure falsehood. It was praised at its launch, but then so was WoD. At this point Legion is being dumpstered on for its complete lack of PVP balance, its focus on repetitive needlessly gated tasks aimed at singleplayer playstyle, its RNG-on-RNG-on-RNG loot system, and its focus on RNG legendaries that make or break class balance. It's hardly being held up anymore as a shining example of the game.