finalflame
Banned
Again, Mercy is highly sought after by the enemy team more than any other character. Obviously every character has to worry about positioning, but don't pretend that for Mercy it is much more important than for most others.
Plenty of characters can do their jobs from a distance. Hanzo, Pharah, Widow, Bastion, Torb's Turret, Symmetra's Turrets, Junkrat, McCree, and so on. These character can get into a position or vantage point, and basically hang out. A good ( and I stress good here) Mercy player is constantly jumping from teammate to teammate determing who is contributing the most damage that might need a boost, or who needs healing.
And I'm sorry but comparing her to Zen is just not the right call. For instance, as a Tracer, if I approach a Mercy, my concern is Mercy leaping to a teammate before I get the kill. If I approach a Zen, my concern is him turning to me and popping me in the head and killing me. Zen has the tools to defend himself at the ready. Mercy does not.
Zen is a 3-star difficulty hero, Mercy is a 1-star difficulty hero. This, in and of it self, should already be telling in the difference between their skill ceilings.
Playing mercy is not trivial, but she has a relatively low skill ceiling compared to the rest of the roster. Not to say playing her is mindless, but it's simply not that hard even at high levels of play. As with Overwatch in general, the game itself takes a lot of thought to play correctly, but this is true for all heroes.