I'll have to reread the Ovid and get back--but your summaries are excellent.

Euripides I'm more familiar with. At the end of his tragedy, Medea exits in a machina typically reserved for gods. The irony is that Euripides is no fan of gods--they lack the human capacity to suffer and empathize with suffering (cf. the endings of Hippolytus and Electra--Aristotle apparently missed the point that Euripides' deus ex machina endings are ironic, not symptoms of lazy writing), and this is what Medea surrenders to get her revenge. So she may escape punishment but she does so at the cost of her humanity. And of course the Greeks (exemplified by Jason) are purveyors of misogyny and xenophobia, under the guise of reason.