to emphasize this: numbers don't win games, situational awareness and understanding your role (tank, dps, heal) wins games. for example, tanks shouldn't be learning "how to boost their prot numbers," they should be learning how to guard swap most effectively, anticipate dps bursts and cc's from the other team, and how to position themselves. and as another example, dps need to learn their class-specific cc's and how they fit into the metagame, as well as how to tell when they should be focused on proc building, vs cc, vs bursting (and on which target!).
anyone can say "here is my rotation. pop dodge when you get a dot on you", but the exceptional players will be able to provide situational awareness advice as well. just my 2cents for potential instructors.