These are not random fighters, these are githyanki. It's totally logical that they would be crazy strong. Consider that Lae'zel at the start of the game is a rookie trainee who hasn't accomplished her rite of passage into adulthood yet (you do that by bringing back a mind flayer's head). These, by comparison, are supposed to be seasoned warriors. Even experienced adventurers who are familiar with their kind would be tempted to turn and run.
