yet it was introduced in the first episode, and seems to have nothing to do with the supernova or the refugees?
The show is called Star Trek: Picard, not Star Trek: Romulans. The story is about Picard dealing with the baggage of his past, including Data's death and his ordeal with the Borg. They tied him in with the Romulan supernova because it was a major (well, the only) established event in post-Nemesis continuity, so they couldn't ignore it. But they still made it about Picard, about his mistakes and regrets that he now has to confront. And they connected it to androids and the Borg so that it would link to the other bits of Picard baggage they wanted him to confront.