No he is not. It's like you automatically associate anything powerful with Sueishness.
Take Death, from Discworld. Anthropomorphic Personification, extremely powerful, at the end of the world it will be his job to turn off the lights, put up the chairs, and lock the door on his way out. He is probably the single most powerful thing on the Disc, but he's not a sue because, despite all that power, he actually has character. Mary Sues are not characters, they are vehicles through which the author lives out his/her fantasies.
Like I said before, sue is how the character behaves and how the narrative reacts to that behavior.
Also, everyone who needs to be told what Phychonauts is needs to slap themselves in the face. That's your punishment for not buying Phychonauts.
Hey son, wanna' learn how ta' make witch balls?