Its not all sleepy wait for cool downs.
For the person actually doing it their watching many things such as cool downs, health and mana bars of other players, buffs trying not to agro other mobs and dealing with them as they add to the mix if they do. Thinking on their feet, what to hit next and what not too..... to the outsider it looks like their doing nothing at all.
-I've seen "great people" that extremely stand out because of what their doing in the backround.
Good tanks and healers stand out, BUT DPS have a huge amount to do with combat also. Often unless someone has a damage meter, IT'S IMPOSSIBLE to give DPS any credit when their infact doing an amazing job.... or not !
-I've been in seemingly equal groups to the person watching. Yet group A is far far better than group B. I've been in groups that could polish off a dungeon easy four levels below another.
Take baseball as a good example, sounds easy and boring yet one is better than the next. Some could say hitting the ball well could be luck the first three times.... But in the long run their's a huge spread among players.