I think the purpose of Farscape is to showcase the talents of the Jim Henson company while having fun and exciting predominantly male fans. It's very much steeped in Geek Cultural which makes sense since it was made for the Sci-Fi channel. I think that watching it now we can read all sorts of depth into it and ways we relate to the characters but that the writers really didn't put as much thought into it all as you are and the point is "wouldn't it be fun if there was a nympho street rat with cleavage." You're supposed to see yourself as John even though many of us see ourselves in Chiana because as trans women we've often had to resort to survival sex work and sugaring to get our needs met. But that's not who wrote the show and not who it was aimed at.
That said, D'argo is hot in ways that particularly appeal to people attracted to men so I guess they anticipated someone besides straight men watching.

