Is Star Wars's treatment of droids and their agency/sentience defensible? How do you think it compares to Star Trek?
question in title
No, but a lot of what Lucas wrote in the Star Wars universe isn't defensible.
I would say no. I mean, the treatment fits the universe (lots of people enslaving other people), but there isn't even a subtle condemnation of this. In many ways, despite it tending to be a story about rebellion, Star Wars mostly tells a story with the status quo; especially in the original trilogy, there's never really an "are we the good guys" moment. (I could be wrong - been ages since I watched anything Star Wars.)
Meanwhile, Star Trek is constantly examining itself, with Starfleet officers often "stop[ping] to debate the rights of a robot" or whether the self-respect of one Starfleet officer is worth the safety of the Alpha Quadrant. Even when they treat synths like crap, it's usually depicted as being morally wrong.
This is a bit of a tangent, but this question makes me think about the evolution of Ood depictions in Doctor Who. Their first appearance was a bit weird about their enslavement, but they rectified that in later episodes.
P.S: I think this question is more suited for c/startrek than Daystrom Institute, as it's more about comparing the themes of two franchises than any in-universe explanation.
Have you seen Solo: A Star Wars Story? It’s addressed pretty head-on in that film.
In Star Wars the droids seem pretty ok with their situation as servants. I suppose you could describe Zora in Discovery similarly, but I'm struggling to think of other examples in Trek.
In the Lucas movies, droids are pretty explicitly portrayed as chattel slaves. They are auctioned off, have separate inferior quarters (Jabba's droid quarters are particularly notable), and are basically treated as beings without agency despite definitely having agency. There's even an explicit visual analogy - Anakin and Shmi have collars that control them and could kill them, and the droids also have (spaceships shaped like) collars that control them and can kill them.