Yes, Olivia, Peter and Walter are the leads. But Olivia is developing superpowers, which makes her nothing like Mulder or Scully, although it does make her a boring comic book heroine. Peter's obtuse disinterest in science, or the Pattern, or a relationship with his father (whom he calls Walter as a signal to the audience) parallels Scully's invincible skepticism in the face of repeated personal experience.
Astrid does not suffer from the adolescent interests of the producers. For that reason she has an engaging, sexy persona that is vastly more interesting than the long suffering, multiply endangered, dream figure of Dunham. Her, you want to see more of. Olivia, you only want to see less clothing of. Despite this, she is a minor character. They ostentatiously introduced a religious FBI girl but she got unceremoniously dumped, unless the followup is ludicrously delayed.