Most games gives you a bunch of classes, which are expanded and polished over the years. Some skills go away, some skills are introduced but the core remains the same.
Now WoW, especially after WotLk seems to not know what they want to do. They change so often and yet are homogeinized.
Legion has done a good job with class fantasy, but all the classes still feel the same at its core - ranged DPS melee DPS tank or Healer. They have also balanced the specs around the artifacts that are getting shelved soon anyway.
You'd think we would have an extremely balanced, polished and heterogeneous set of classes and specs after so many years, where classes are easy to use and hard to master, but we are, dare I to say, worse than in vanilla WoW on class design.