If the entire focus of a challenge is on challenging the player, what is the point of having a character at all? If switching from one character to another has no appreciable difference in the encounters, as all encounters will be directed towards Brendan and not Kelleshan or Arqos or any of my characters, then what's the point in making a character?
The point of having characters is a point of contract that players sign among them so that this can be based on explicit rules. Since a roleplaying game is a social game this better be made explicit by the rules so the need for different characters.