It seems as though mages are generally the most powerful class in any RPG, whether it's on paper or on the screen.
This is true.
There's a very human reason for that behavior as well.
Picking locks? That's real. I can do it. I know what is and isn't possible for a lock. Thus, I know the limits.
Swinging a sword? We know what that does, and we know the limits. No one on Earth can swing a sword hard enough to make a pony appear out of thin air.
But "magic..." What is that? What limits does it have? "NONE! IT'S MAGIC!"
That's why it's overpowered - because we perceive it as imagination and limitless. Many game creators (and players) fail to acknowledge the issue of balance or of realistic limits. Even if magic were real, it would have limits - limits that both game creators and the players have historically failed to impose on their players or themselves.