Her role as a prop for Thanos conflicting emotion is not much more different than Loki, whom sole purpose was to establish how manical, brutal, & merciless he is, in achieving his goal.
I didn't really pick up on it when I watched the film, partially because, yes, there are other characters who serve a similar role, like Loki.
However, ask yourself: what are the female heroes doing in this movie? What are their roles?
Gamora is the most prominent one. Her death is the pivotal moment in the protagonist's arc. Nebula's main thing is being tortured, as part of the dynamic between Thanos and Gamora.
Black Widow's role is entirely forgettable. Okoye is more memorable, but only because she steals a couple of scenes.
Wanda's role probably has the most substance, outside of Gamora.
So it's really hard to compare Gamora to Loki, in the sense that all of the heroes who have prominent roles in the film are male. Starlord, Tony, Strange, Spider-Man and Thor, especially.
I wouldn't dismiss the film on that basis, and I didn't really come out of the theater thinking about it, but I can understand why some people might not be too thrilled with that aspect of the film. They really need some female heroes who actually play pivotal roles (Captain Marvel).
I think as dudes watching the film, we are less likely to notice or be bothered by it.
Im not at all bothered about it & thought the interaction between the two, Gamora & Thanos was the most humanistic part of the film in a very strange way...because we are talking a war criminal, committing acts of genocide & abduction.
I agree that the scenes are effective from that point of view, but the point seems valid to me.