ocr classics greek theatre slavery questions

hi there, i do a-level classical civilisation with ocr, doing greek theatre (oedipus rex, bacchae and frogs) and the world of the hero.
very confused on what to write for this 20 marker -
evaluate the importance of the treatment of slaves to the success of the greek tragedies you have studied.
i know i would structure it in three paragraphs - one focusing on plot, one on characterisation and one on themes - but not sure what to write for each.
pls reply asap!!!

I‘d probably link the treatment of slaves to descent into tyranny — as Oedipus tortures the messanger we can see that Oedipus has became a tyrant, which can then be linked to politics, making the play engaging and therefore successful. This also contrasts how well Oedipus treated his citizens at the beginning and was willing to take advice from the elderly. Pentheus‘ views vastly differ from his citizens — a soldier reports that ve told Dionysus he was only arresting him to avoid Pentheus‘ wrath.
Pentheus also refers to his citizens as slaves (line 669) — shows how there is a complete loss of democracy in Thebes.
Could counter this by saying that there aren’t exactly any slaves in these tragedies, only soldiers and messangers.
Overall, the treatment of slaves in these tragedies helps to make them politically engaging, so they are also successful