This is what I thought, because I am a expert in plot twist and I thought they meant death or the end of something else but the beginning of something else as well.
The "Harbinger of Death" Explained
Kara does not lead the human race to its end as one would initially think. It seems that by "end" the hybrid meant not their destruction but their goal, seeing as she actually leads Humanity to a new home and saves them from extinction.
However, since all of today's humans are distant descendants of Hera Agathon, the "pure" human race did in fact come to an end over the generations that followed. Furthermore, by abandoning its advanced technology and making peace with the Cylons, Colonial Humanity came to an end and started over from scratch as Earth Humanity.
Kara being the "harbinger of death" can also be explained as her having died and then being brought back to life. Thus, she is "living proof" of the notion that everything dies and that there is life after death. This is evidenced by her role in the events leading up to the destruction of the Cylon Hub.
It is not entirely clear why the First Hybrid did not want the human race to follow Kara. One possibility is that he did not want humans and Cylons breeding together. Another possibility is that he wanted the Cycle of violence to continue for some reason. It is also not clear why Kendra Shaw was given this warning only to have her message to Pegasus jammed.
This might also help explain.
She was sort of the herald of the apocalypse because her leading everyone to the end did bring about a lot of death. Also, didn't she put the last coordinates in that ended the long journey.
I think people were expecting to much death and that is why they were surprised when it wasn't a full on apocalypse with everyone dead.
A deleted scene included in the extended DVD cut shows Starbuck and Helo getting drunk at Joe's Bar, and Starbuck ruminating on her destiny as the Harbinger of Death. She says finding nuked Earth pretty much fulfilled that part of the plan and she wonders what her purpose is now.
Helo suggests other meanings for Harbinger, such as herald, to suggest her destiny could be positive. This scene foreshadows Starbuck's use of the music to find the second Earth in "Daybreak," and implies her role in leading the human race to its end refers to finding the planet where human and Cylon can live a blended existence.
Also there is a picture you can observe from this link.
From this picture a lot of people died, due to the harbinger of death who saved and condemned loads of people.