The portraits of Clytemnestra in Aeschylus’ Agamemnon and Medea in Euripides' Medea do not necessarily reflect what would have been the playwrights' attitudes towards ordinary women in classical Athens in any straightforward way, as the narratives on which the stories are based descend from the Bronze Age or earlier. Also, Medea is a foreign sorceress and Clytemnestra a powerful woman directly descended from the gods.
One thing the two women do have in common is that they are powerful and evil. In general, women (other than goddesses) in epic and tragedy who have power tend to be evil and/or come to bad ends, a general point illustrated by the Chorus' speech in Aeschylus’ Agamemnon:
 O Fiend who falls upon this house and Tantalus' two descendants, you who by the hands of women exert a rule matching their temper, a rule bitter to my soul! Perched over his body like a hateful raven, in hoarse notes she chants her song of triumph.
Thus one might deduce that there was a general presumption that women should not be trusted with political power, a presumption supported by the fact that they had almost no political power in classical Athens.