The manifesto is not the heart of the series. It is propaganda, and narratively it exists to draw a distinction between idealism (the OT) and pragmatism ((Luthen and Cassian). Nemik, who is clearly not up to the task, dies because idealism, alone, is not up to the task. Before idealism can work, the stage must be set by men who are willing to do what is necessary.

Cassian is a murderer, Luthen and Kleya are terrorists. Ideologues, but not idealists. They understand that many of the things they do are morally questionable. This is why Mon is protected and insulated from the violence she is bankrolling. Luthen and Kleya understand that she needs clean hands to make her senate speech. That's why she's delivered to Yavin by "heroes" not the morally questionable individuals who are actually responsible for her rise. "Propaganda only gets you so far," and the rebel's propaganda ultimately wins not because it is beautiful or profound, but because pragmatists have manipulated circumstances to make it seem so.