Euripides' Theseus condemned himself. The differences between the two plays let us understand the earlier model. They show how the earlier myth can be adapted for modern times. The stepfather is pure evil. He is not a tragic figure, but is comparable to villains like Aegisthus, or Odysseus in Philoctetes , or Agamemnon and Menelaus in Ajax , or Menelaus in Orestes that Aristotle faults for his evil.
Tragic figures are best in their combination of good and evil.
Then when we think about it, we realize that this is also what Euripides did. Theseus might have had the same reservations about Hippolytus asking for his first chariot that we do about our children asking for their first car. Euripides' play was about a teenager who knew it all, and showed what happened when ignorance escalated. The misunderstanding on the mother's part is also, obviously, not to be minimized. This myth shows us how destructive lies can be.